cannot print double-sided pages anymore

[Removed by request]

Binary package hint: cups

I own an HP Photosmart C6280 printer, which is normally capable of double-sided printing.
I am on Jaunty, kernel version 2.6.28-11
cups 1.3.9

I have been able to print double-sided pages until the last update: since then, the printer starts and correctly prints the first page, then it just stops when it should turn the page and start printing on the other side. The sheet stays in the machine until I cancel the operation.

I get this message on the status window
usr/lib/cups/filter/foomatic-rip failed

and this is the error log

[CGI] Unable to scan "@LOCAL"!
CUPS-Add-Modify-Printer: Unauthorized
PID 3964 (/usr/lib/cups/filter/foomatic-rip) stopped with status 9!
[Job 11] Job stopped due to filter errors.

ProblemType: Bug
Architecture: i386
DistroRelease: Ubuntu 9.04
Lpstat: dispositivo per Photosmart-C6200-series: hp:/usb/Photosmart_C6200_series?serial=MY87EHH1850506
MachineType: ASUSTeK Computer Inc. N51Vg
NonfreeKernelModules: nvidia
Package: cups 1.3.9-17ubuntu3
Papersize: a4
PpdFiles: Photosmart-C6200-series: HP Photosmart c6200 Series hpijs, 3.9.4b
ProcCmdLine: root=UUID=01593879-c788-4c5d-a74b-c891cfdd6248 ro quiet splash
ProcEnviron:
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.28-11.42-generic
SourcePackage: cups