Strange Error After Log In

I've just come across an error that I have never encountered before.

After logging into an account, you are taken to the profile page for the account. If I click the Upload link from that page, it takes me to the signup.php page, where you can either sign up or sign in. I try to sign in again, and the page just reloads. This only happens if I click on Upload from the profile page. Is this an error with the code for that page?

Update:

Upon further inspection, it looks like this problem is a little more widespread than I had thought. Whenever I log in, instead of seeing the user name/inbox in the header, it still says Sign Up and Log In. It must not be recognizing that I'm logged in. I have not made any kind of major revisions to the site. Nothing except the valign="top" on new videos and recently viewed. That shouldn't be causing this.

Is there someone on the server side I should check into? I know they just spent a day and a half doing maintenance on the server. Is there a setting I should ask them to double check?

I sent a ticket in to Level 2 support on this issue, which normally ends up going to level 3 (System Admin). The problem is now automagically fixed. Not sure if they switched a setting or what.