[Dovecot] failed to create storage data

Hello,

I have a problem. I get the message 'Failed to create storage with data' I have 2 emailaccounts which are working perfect and that worked fine. But now I want to add another account and now it said 'Failed to create storage with data' What is the problem?

I have the same rights on the directory and it worked first fine. I didn't changed it. Can any one point me in the good direction?

I use dovecot with mysql and postfix.

thanks in advance,

Alex