I have the same issue.
Background:
Debian 64bit Squeeze, ISPConfig 3 Control Panel, Apache2, PHP 5.3.X.X
I use the following for my system:
/osticket-new - folder where all the new goodies are
/osticket-old - folder where the last working version of osticket is stored
/support - soft link ( ln -s osticket-new support )
Now this worked fine up until the latest "patch" - 1.7.1.1 - so 1.7.1 works fine.
Upon installing 1.7.1.1 it comes up with the same error as everyone else is having or it just gets stuck on the login page.
Talk about frustrating. Anyway 1.7.1 works fine for me as of now. Try a downgrade guys.