Error: Unable to update hosting preferences: Unable to create system user: usermng:

[timsnet]

this was working fine yesterday but now when i create a domain through my plesk control panel i get the error:

Error: Unable to update hosting preferences: Unable to create system user: usermng: Unable to add user: homediscount

when trying to setup physical hosting. It doesnt seem to matter what the username i specify is (for ftp access). It always fails... how do i fix this problem, nothing haas been changed on the plesk server as far as i know?