Session Verification Failed when installing new theme

[Jerri Blank]

I just installed 2.0 RC 5 and am using the core theme.  When I try to install a new theme from the .zip file I've downloaded to my computer, I get the old "session verification failed" error.  The same thing happens when I just try to switch the board from one theme to another.  I've changed the cookie name, I've deleted my cookies, I've checked the error log and found nothing, etc. etc.  I even FTP'd the theme to my server and am trying to install it from there.  Same deal.

I upgraded last night, and the only mod I've installed since is Stop Forum Spam.

Any idea what's causing this?

[Joker™]

What are the files and folder permissions?