Internal Server Error with some actions in WP 2.6.5

Hi ppl,

I have successfully installed a 2.6.5 copy of WP on my host, but with a few actions I get a 500 Internal Server Error on my screen. Now I know what it means, something made the server freak out due to a misconfiguration. But, what I find quite strange, is that it only appears when doing specific tasks. I can replicate it with three situations so far:

– Automatic update of plugins over FTP (after entering login credentials)
– Changing the Role of a user and submitting the changes
– Changing the display name of a user and submitting the changes

All other actions are just fine. Does anyone have a clue what to do about that?