Cannot create accounts (account status is not ok)

[Numicus]

"Did you deleted the old ispCP and after reinstall that? You must remove the vu* gorup and user from the system before you create a new domain (except the vu2000)"
What exactly do you mean by that?

I uninstalled using the ispCP uninstaller, it gave an error though, I deleted some folders manually. It may be that it did not delete the users/groups.
Should I dedelete al vu* groups in etc/groups?

UPDATE: deleted the vu* groups, the error changed now:
sys_command() | ERROR: External command '/usr/sbin/useradd -c virtual-user -d /var/www/virtual/zennid.nl -g vu2003 -s /bin/false -u 2003 vu2003' returned '9' status !

Looks like I need to remove the users..in which file will I find them / which command to run to delete them?