When a website management user is setup for an virtual host they are assigned the the same UID as the owner of the site. This dose not cause a problem with webmin or virtualmin but causes problems with Yast user and group module. When Yast calls this module it checks the /etc/passwd file and flags this error.
Error: There are muliple users with the same UID ('1001') in the /etc/passwd. Correct them manually before running the Yast users or group module again.
The same error is flaged when the group module is called.