Redmine

Yesterday I've updated our redMine to the latest stable release using the svn trunk (http://redmine.rubyforge.org/svn/branches/0.8-stable). I've done this just like many times before and it always worked for me. I've migrated database, installed gems and everything else.
Now that I updated to 0.8.5 everything seemed to work fine. But today I wanted to add a new project and all I get is an internal (server?) error.

Internal error

An error occurred on the page you were trying to access.
If you continue to experience problems please contact your redMine administrator for assistance.

Since I am more a PHP-guy and not used to Ruby and stuff I can't manage to fix it on my own. I've tried restarting the mongrel server but it didn't help at all. So I just started the older version of redMine which I've thankfully kept in place and created the new project using this older version.

So now... what you expect me to do?
Should I do the whole update-process again or has this problem occured yet somewhere else?

Thanks a lot,
Gerrit Fries