I also get a problem.
I am running:

GNU Emacs 23.3.1 (i386-mingw-nt5.1.2600)
 of 2011-03-10 on 3249CTO

I downloaded web-vcs.el from the link you provide here: http://bazaar.launchpad.net/~nxhtml/nxhtml/main/annotate/head%3A/web-vcs.el

using the Download File button in the upper right-hand corner.
-------------------------

My web-vcs-log.org is:


* 2011-10-21
** Downloading file 17:30:32 GMT
   file [[file:d:/My Documents/.emacs.d/autostart.el][d:/My Documents/.emacs.d/autostart.el]]
   from http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110313013000-drl16yyp60auegw9/autostart.el-20080724174035-zgon4j679232cch3-2/autostart.el

----------------------------

My *Messages* output is:


Welcome to install nXhtml.
First the nXhtml specific web install file must be downloaded.
You will get a chance to review it before it is used.

Do you want to continue? (y or n) 
(New file)
OVERVIEW
Contacting host: bazaar.launchpad.net:80
HTTP/0.9 How I hate thee!
Entering debugger...
Wrote d:/My Documents/.emacs.d/web-vcs-log.org
HTTP/0.9 How I hate thee!
error in process filter: url-http-generic-filter: Wrong type argument: number-or-marker-p, nil
error in process filter: Wrong type argument: number-or-marker-p, nil
HTTP/0.9 How I hate thee!
error in process filter: url-http-generic-filter: Wrong type argument: number-or-marker-p, nil
error in process filter: Wrong type argument: number-or-marker-p, nil
HTTP/0.9 How I hate thee!
error in process filter: url-http-generic-filter: Wrong type argument: number-or-marker-p, nil
error in process filter: Wrong type argument: number-or-marker-p, nil
HTTP/0.9 How I hate thee!
error in process filter: url-http-generic-filter: Wrong type argument: number-or-marker-p, nil
error in process filter: Wrong type argument: number-or-marker-p, nil
HTTP/0.9 How I hate thee!
error in process filter: url-http-generic-filter: Wrong type argument: number-or-marker-p, nil
error in process filter: Wrong type argument: number-or-marker-p, nil
byte-code: Beginning of buffer [3 times]
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
Quit
read-buffer-to-switch: Command attempted to use minibuffer while in minibuffer
posn-set-point: Position not in text area of window
Saved text from "Debugger entered--Lisp error: (wrong-typ"


-------------------




My backtrace is (sorry about the yucky paste):

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  url-http-wait-for-headers-change-function(1 3 2)
  url-http-generic-filter(#<process bazaar.launchpad.net> "
\n")
  accept-process-output(#<process bazaar.launchpad.net>)
  byte-code("\302\303	!)\207" [inhibit-quit proc nil accept-process-output] 2)
  url-retrieve-synchronously("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110313013000-drl16yyp60auegw9/autostart.el-20080724174035-zgon4j679232cch3-2/autostart.el")
  (let ((buffer ...) (handle nil) (ret nil)) (if (not buffer) (error "Retrieving url %s gave no buffer" url)) (with-current-buffer buffer (if ... ... ... ... ... ... ...)) ret)
  web-vcs-url-copy-file("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110313013000-drl16yyp60auegw9/autostart.el-20080724174035-zgon4j679232cch3-2/autostart.el" "d:/My Documents/.emacs.d/TEMPORARY-WEB-AUTO-LOAD-autostart.el" nil t)
  (setq http-sts (web-vcs-url-copy-file file-url dl-file nil t))
  (let ((http-sts nil) (file-nonempty nil) (fail-reason nil)) (when dest-file (web-vcs-log file-url dest-file nil)) (web-vcs-display-messages nil) (setq http-sts (web-vcs-url-copy-file file-url dl-file nil t)) (if (and ... ... ...) (when dest-file ...) (setq fail-reason ...) (unless dest-file ...) (web-vcs-log nil nil ...) (web-vcs-message-with-face ... "Download failed: %s, %S" fail-reason file-url) (web-vcs-display-messages t) (when ... ...) (message "\n") (web-vcs-message-with-face ... "Please retry what you did before!\n") (throw ... nil)))
  web-vcs-url-copy-file-and-check("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110313013000-drl16yyp60auegw9/autostart.el-20080724174035-zgon4j679232cch3-2/autostart.el" "d:/My Documents/.emacs.d/TEMPORARY-WEB-AUTO-LOAD-autostart.el" "d:/My Documents/.emacs.d/autostart.el")
  (cond ((and dl-file-time url-file-time ... ...) (web-vcs-message-with-face ... "Local file %s is newer or same age" file-rel-name)) (t (while ... ... ...) (when ... ...) (web-vcs-url-copy-file-and-check url-file temp-file dl-file-name) (let* ... ... ... ... ... ...)))
  (let* ((url-file ...) (url-file-time-str ...) (url-file-time ...) (url-file-name-regexp ...) (url-file-rel-name ...) (dl-file-name ...) (dl-file-time ...) (file-rel-name ...) (file-name ...) (temp-file ...) temp-buf) (cond (... ...) (t ... ... ... ...)) (redisplay t))
  (while --cl-dolist-temp-- (setq file (car --cl-dolist-temp--)) (let* (... ... ... ... ... ... ... ... ... ... temp-buf) (cond ... ...) (redisplay t)) (setq --cl-dolist-temp-- (cdr --cl-dolist-temp--)))
  (let ((--cl-dolist-temp-- ...) file) (while --cl-dolist-temp-- (setq file ...) (let* ... ... ...) (setq --cl-dolist-temp-- ...)) nil)
  (catch (quote --cl-block-nil--) (let (... file) (while --cl-dolist-temp-- ... ... ...) nil))
  (cl-block-wrapper (catch (quote --cl-block-nil--) (let ... ... nil)))
  (block nil (let (... file) (while --cl-dolist-temp-- ... ... ...) nil))
  (dolist (file (reverse files)) (let* (... ... ... ... ... ... ... ... ... ... temp-buf) (cond ... ...) (redisplay t)))
  web-vcs-download-files((lp "http://www.launchpad.com/ uses this 2010-06-26 with Loggerhead 1.17 (generic?)" ((time 1) (url 2) (patt "\\(?:<td class=\"date\">\\([^<]*?\\)</td>\\(?:.\\|\n\\)*?<a href=\"\\(/~nxhtml/nxhtml/main/download/[^\"]*\\)\" title=\"Download\\)")) "\\(?:<td class=\"autcell\"><a href=\"\\(.+?/files/head:/[^\"]+?\\)\">\\)" "\\([^/]*\\)$" "\\(?:for revision[[:space:]]+<span>\\([[:digit:]]+\\)</span>\\)" "\\(?:/\\([[:digit:]]+\\)\"[^>]+>\\(?:Release \\)?[[:digit:]]+\\.[[:digit:]]+<\\)") (("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110618233059-jb2q3txw21aleow6/webvcs.el-20091227180846-favloh4bvxp3i0mh-4/web-vcs.el" "2011-06-18 23:30:59") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20101219013302-uc6gbtmhecqw8ve2/webautoload.el-20091227180846-favloh4bvxp3i0mh-3/web-autoload.el" "2010-12-19 01:33:02") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110316010700-b7mttztbuoch7z8l/readme.txt-20091201225055-ijilnjhor5wc5s03-1/README.txt" "2011-03-16 01:07:00") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20100627022309-6em45v2czlwyjrgk/nxhtmlmaint.el-20090101213540-jlah6xe0n65g93pw-3/nxhtmlmaint.el" "2010-06-27 02:23:09") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110504235300-ojqwz9z1bxm5dona/nxhtmlwebvcs.el-20100113172514-fyszxn1ypx4ml96h-2/nxhtml-web-vcs.el" "2011-05-04 23:53:00") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110504235300-ojqwz9z1bxm5dona/nxhtmlloaddefs.el-20080927190633-bvdatx6qc6m3ze5h-1/nxhtml-loaddefs.el" "2011-05-04 23:53:00") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20101228200718-9wwuyehbvtygvstb/nxhtmlbase.el-20100113172514-fyszxn1ypx4ml96h-1/nxhtml-base.el" "2010-12-28 20:07:18") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20090101213554-u78qtp1mw0225vzq/emacs22.cmd-20090101213540-jlah6xe0n65g93pw-2/emacs22.cmd" "2009-01-01 21:35:54") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20100118135750-uoj5q7chz82hzazn/autostart22.el-20090101213540-jlah6xe0n65g93pw-1/autostart22.el" "2010-01-18 13:57:50") ("http://bazaar.launchpad.net/~nxhtml/nxhtml/main/download/lennart.borgman%40gmail.com-20110313013000-drl16yyp60auegw9/autostart.el-20080724174035-zgon4j679232cch3-2/autostart.el" "2008-12-26 14:22:34")) "d:/My Documents/.emacs.d/" "d:/My Documents/.emacs.d/")
  (let* ((files-matcher ...) (dirs-href-regexp ...) (revision-regexp ...) (dl-dir ...) (lst-dl-relative ...) (lst-file-mask ...) this-page-revision files suburls (moved 0) (temp-file-base ...) temp-list-file temp-list-buf folder-res http-sts) (web-vcs-display-messages nil) (unless (file-directory-p dl-dir) (make-directory dl-dir t)) (setq temp-list-file (make-temp-name temp-file-base)) (setq temp-list-buf (web-vcs-ass-folder-cache page-url)) (unless temp-list-buf (let ... ...)) (with-current-buffer (car folder-res) (when dl-revision ...) (when dl-revision ...) (goto-char ...) (let ... ...) (when ... ...) (when recursive ... ...) (kill-buffer)) (web-vcs-download-files vcs-rec files dl-dir dl-root) (when suburls (dolist ... ...)) (list this-page-revision moved))
  web-vcs-get-files-on-page-1((lp "http://www.launchpad.com/ uses this 2010-06-26 with Loggerhead 1.17 (generic?)" ((time 1) (url 2) (patt "\\(?:<td class=\"date\">\\([^<]*?\\)</td>\\(?:.\\|\n\\)*?<a href=\"\\(/~nxhtml/nxhtml/main/download/[^\"]*\\)\" title=\"Download\\)")) "\\(?:<td class=\"autcell\"><a href=\"\\(.+?/files/head:/[^\"]+?\\)\">\\)" "\\([^/]*\\)$" "\\(?:for revision[[:space:]]+<span>\\([[:digit:]]+\\)</span>\\)" "\\(?:/\\([[:digit:]]+\\)\"[^>]+>\\(?:Release \\)?[[:digit:]]+\\.[[:digit:]]+<\\)") "http://bazaar.launchpad.net/~nxhtml/nxhtml/main/files/head:/" "d:/My Documents/.emacs.d/" "" "nxhtml-web-vcs.el" 0 nil nil 0)
  (let ((vcs-rec ...)) (web-vcs-get-files-on-page-1 vcs-rec url dl-dir "" file-mask 0 nil nil num-files))
  web-vcs-get-missing-matching-files(lp "http://bazaar.launchpad.net/~nxhtml/nxhtml/main/files/head:/" "d:/My Documents/.emacs.d/" "nxhtml-web-vcs.el" 0)
  (if (file-exists-p (cdr file)) nil (web-vcs-get-missing-matching-files (quote lp) root-url this-dir (car file) 0))
  (unless (file-exists-p (cdr file)) (web-vcs-get-missing-matching-files (quote lp) root-url this-dir (car file) 0))
  (while --cl-dolist-temp-- (setq file (car --cl-dolist-temp--)) (unless (file-exists-p ...) (web-vcs-get-missing-matching-files ... root-url this-dir ... 0)) (setq --cl-dolist-temp-- (cdr --cl-dolist-temp--)))
  (let ((--cl-dolist-temp-- files2) file) (while --cl-dolist-temp-- (setq file ...) (unless ... ...) (setq --cl-dolist-temp-- ...)) nil)
  (catch (quote --cl-block-nil--) (let (... file) (while --cl-dolist-temp-- ... ... ...) nil))
  (cl-block-wrapper (catch (quote --cl-block-nil--) (let ... ... nil)))
  (block nil (let (... file) (while --cl-dolist-temp-- ... ... ...) nil))
  (dolist (file files2) (unless (file-exists-p ...) (web-vcs-get-missing-matching-files ... root-url this-dir ... 0)))
  (let* ((this-dir ...) (root-url ...) (files ...) (files2 ...) need-dl) (dolist (file files2) (unless ... ...)) (when need-dl (let ... ...)) (message nil) (unless (get-buffer-window "*Messages*") (web-vcs-display-messages t) (delete-other-windows)) (dolist (file files2) (unless ... ...)) (load (cdr ...)))
  (catch (quote command-level) (setq debug-on-error t) (let* (... ... ... ... need-dl) (dolist ... ...) (when need-dl ...) (message nil) (unless ... ... ...) (dolist ... ...) (load ...)) (call-interactively (quote nxhtml-setup-install)))
  web-vcs-nxhtml()
  call-interactively(web-vcs-nxhtml t nil)
  execute-extended-command(nil)
  call-interactively(execute-extended-command nil nil)