Theme Editor help needed

Since upgrading to 2.9 i get this message when clicking on a file in the theme editor: Oops, no such file exists…

The files are there by the way.

I reinstalled wordpress again, didnt help,

I tried the standard theme, didnt help,

I deactivated all plugins, didnt help.

I posted a topic on the other wordpress section, but nobody replies, also i have seen like 5 of pretty much the same topics discribing this same problem, with no replies.

So i am putting my hope here, that somebody will be able to help here…