Delition of Domains doesn´t work

[The Habit]

Good Evening,

i'm Usind a Fedora Core 4 Root-Server of the 1&1 Internet AG Germany. Sinse im Using Plesk with Fedora 4, i have problems with the configuration and technics.

See, my problem is:

Unable to delete hosting: Unable to delete system user: SysUser->systemRemove() failed: usermng failed: usermng: Unable to set quota for user 'MyUser'

That was the first error i've become. So, i thought: You should delete the User manually-> i'd do it. After the manually delition of the User, i've tried to delete the Domain. Now i become the Error:

Unable to delete hosting: Unable to delete system user: SysUser->systemRemove() failed: usermng failed: usermng: Unable to getpwnam for user MyUser usermng: Error: invalid user 'MyUser'

I didn´t know any working fix, i dont know what should i do. Its realy important to delete the Domain - i hope You can and will help. I'm very thankful about every help!

Thanks and greetings,
Oliver