[Typo3] BE List - mysql warnings

[racco]

hello list!

when I click on List in the backend I have those warning messages 
displayed on my screen:

Warning: mysql_fetch_row(): supplied argument is not a valid MySQL 
result resource in [...]/typo3/t3lib/class.t3lib_db.php on line 754

Warning: Cannot modify header information - headers already sent by 
(output started at [...]/typo3/t3lib/class.t3lib_db.php:754) in 
[...]/typo3/template.php on line 601


what is wrong??

greetings
racco