I am unable to remove a user from the Domain Users group ...

In ADUC, I set a new primary group
When I go to delete I get :
The following Active Directory Serverices error occured : the data is

In C1, I get :
Error -602 the requested proprty / value could not be found

In iManager, I get No error message but the group contimues to appear
after refresh

OES 11 SP2