I think I got this bug. I don't know what exactly causes this problem though...
Using iMac Mid2010, rEFIt 0.14, ubuntu-11.04-alternative-amd64.
Here's my ~/.xsession-errors:
~/.xsession-errors
/etc/gdm/Xsession: Beginning session setup...
/etc/gdm/Xsession: 301: ls: not found
/etc/gdm/Xsession:
Aaw, this was because of my mistake, not this bug.
I just unexpectedly overrode my ~/.profile with wrong PATH and that caused
login failure.
Sorry for bothering!
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