Not sure if its a bug

Rigt after i updated to 1.3.6 I got this:

The server encountered an internal error and was unable to complete your request.

Error message:
Premature end of script headers: store_manager.php

If you think this is a server error, please contact the webmaster.

Error 500

It hapenes only when i want to update attribute values in Store Manager. Other "resets" work fine.

Any Ideas??

Adam