Comment 19 for bug 835310

I think the problem is with PAM, in particular with the package libpam-smbpass. I tried with a clean installation of 11.10, and fast user switching was working ok, but after installing libpam-smbpass it stopped working, exhibiting the same behaviors described above. I may add that lightdm is crashing with the following messages in dmesg:

[ 147.709200] lightdm[1920]: segfault at 0 ip (null) sp 00007f4d965e9c78 error 14 in lightdm[400000+27000]
[ 147.709889] init: lightdm main process (922) killed by SEGV signal

Removing libpam-smbpass restored the correct behavior. Note that switching to the guest account (which does not require authentication) always works, both with and without libpam-smbpass.