Cannot add a new user to CRM 4.0

if adding user in crm is not possible means giving error, follow the followings

#1 you should have the privileg to ccreate user.
#2 check whether the user has been created and disabled
#3 finally On the CRM Server check the following in the Registry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSCRM you should set a registry key AutoGroupManagementOff to value 1 (false).

Sudhanshu