sudden logout while playing 0ad game

[ekrc]

I'm using 12.04. I also have 0ad game installed. Nowadays, while I play 0ad, suddenly the system logs me out and asks me to username/password. I also recognized this warning during logout process:

Modprobe webcamstudio failed. Please use 'dmesg' to find out why

I removed webcamstudio and its requirements but it happens again. I can't understand that what's wrong?

[dino99]

you should find errors/warnings helping you inside .xsession-errors or /var/log/ or /var/crash/

[ekrc]

you should find errors/warnings helping you inside .xsession-errors or /var/log/ or /var/crash/

/var/crash/ was empty
.xsession-errors didn't include log related with this problem
/var/log/ there was no log related with this problem
the problem goes on