I got the same error when clients are accessing the samba server at random occurrences it happens few times a day

lsb_release -rd
Description:	Ubuntu 11.04
Release:	11.04

uname -a
Linux 2.6.38-10-generic #46-Ubuntu SMP Tue Jun 28 15:07:17 UTC 2011 x86_64 GNU/Linux

apt-cache policy samba
samba:
  Installed: 2:3.5.8~dfsg-1ubuntu2.2
  Candidate: 2:3.5.8~dfsg-1ubuntu2.2
  Version table:
 *** 2:3.5.8~dfsg-1ubuntu2.2 0
        500 http://archive.ubuntu.com/ubuntu/ natty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2:3.5.8~dfsg-1ubuntu2 0
        500 http://archive.ubuntu.com/ubuntu/ natty/main amd64 Packages


Thread debugging using libthread_db enabled]
0x00007f9b6bb191ae in waitpid () from /lib/x86_64-linux-gnu/libc.so.6
#0  0x00007f9b6bb191ae in waitpid () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007f9b6baadd6e in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x00007f9b6e9fec53 in smb_panic (why=<value optimized out>) at lib/util.c:1471
#3  0x00007f9b6e9ee2e9 in fault_report (sig=11) at lib/fault.c:52
#4  sig_fault (sig=11) at lib/fault.c:75
#5  <signal handler called>
#6  0x00007f9b6baee5d1 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#7  0x00007f9b6e9d511e in rep_strlcpy (d=0x7fff13d66918 "", s=0x0, bufsize=256) at ../lib/replace/replace.c:69
#8  0x00007f9b6ea0b434 in connections_fetch_entry (mem_ctx=0x0, conn=0x7f9b7094c920, name=0x0) at lib/conn_tdb.c:65
#9  0x00007f9b6e78c676 in yield_connection (conn=0x7f9b7094c920, name=0x0) at smbd/connection.c:33
#10 0x00007f9b6e7fd7f6 in close_cnum (conn=0x7f9b7094c920, vuid=101) at smbd/service.c:1256
#11 0x00007f9b6e7b916d in reply_tdis (req=0x7f9b70955b00) at smbd/reply.c:4912
#12 0x00007f9b6e7f8bb5 in switch_message (type=113 'q', req=0x7f9b70955b00, size=39) at smbd/process.c:1404
#13 0x00007f9b6e7f8f57 in construct_reply (inbuf=<value optimized out>, nread=39, unread_bytes=0, seqnum=0, encrypted=false, deferred_pcd=0x0, conn=<value optimized out>) at smbd/process.c:1436
#14 process_smb (inbuf=<value optimized out>, nread=39, unread_bytes=0, seqnum=0, encrypted=false, deferred_pcd=0x0, conn=<value optimized out>) at smbd/process.c:1509
#15 0x00007f9b6e7f93da in smbd_server_connection_read_handler (ev=<value optimized out>, fde=<value optimized out>, flags=<value optimized out>, private_data=<value optimized out>) at smbd/process.c:2126
#16 smbd_server_connection_handler (ev=<value optimized out>, fde=<value optimized out>, flags=<value optimized out>, private_data=<value optimized out>) at smbd/process.c:2141
#17 0x00007f9b6ea0e303 in run_events (ev=0x7f9b7086d430, selrtn=1, read_fds=0x7fff13d66d90, write_fds=0x7fff13d66d10) at lib/events.c:157
#18 0x00007f9b6e7fa936 in smbd_server_connection_loop_once () at smbd/process.c:844
#19 smbd_process () at smbd/process.c:2455
#20 0x00007f9b6ecf991e in smbd_accept_connection (ev=<value optimized out>, fde=<value optimized out>, flags=<value optimized out>, private_data=<value optimized out>) at smbd/server.c:438
#21 0x00007f9b6ea0e303 in run_events (ev=0x7f9b7086d430, selrtn=1, read_fds=0x7fff13d670b0, write_fds=0x7fff13d67030) at lib/events.c:157
#22 0x00007f9b6ea0e4f8 in s3_event_loop_once (ev=0x7f9b7086d430, location=<value optimized out>) at lib/events.c:220
#23 0x00007f9b6ea0ef90 in _tevent_loop_once (ev=0x7f9b7086d430, location=0x7f9b6ef000c8 "smbd/server.c:726") at ../lib/tevent/tevent.c:497
#24 0x00007f9b6ecfa5c3 in smbd_parent_loop (argc=<value optimized out>, argv=<value optimized out>) at smbd/server.c:726
#25 main (argc=<value optimized out>, argv=<value optimized out>) at smbd/server.c:1316
A debugging session is active.

       Inferior 1 [process 4958] will be detached.

Quit anyway? (y or n) [answered Y; input not from terminal]