[TYPO3] Typo3 4.0: Mysql errors both in backend and in frontend

[Kevin Renskers]

Hi list,

After I upgraded to the newest Typo3 I am getting this Mysql error in a 
couple of places:

Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL 
result resource in /home/admin/typo3_src-4.0/t3lib/class.t3lib_db.php on 
line 801

In the backend, I get this error when I go to the 'view record change 
history' page and *any* page viewed from the List module.

In the frontend I get the error on pages with the (newest version of 
the) sr_feuser_register plugin on it.

I have no clue what could be wrong here :(
Kevin Renskers