[vchkpw] user authentication fails

[Ender]

Hi all.   We have qmail-vpopmail-qmailadmin mail server with mysql. There were no problems about authentication of users. A few days ago the problems occured. Users can not log in to pop server. When I looked at the logs I saw the below line:   Feb 5 11:55:54 server vpopmail[20400]: vchkpw: vpopmail user not found [EMAIL PROTECTED]   What can be the problem? And what to do for solution? Could you please help me? Thanks...   Ender