Domain Security Policy

Hi,
Whenever I open Domain Security Policy in Administrative Tools I get a message stating that
“Failed to open the group policy object. You may not have appropriate rights.”
” The system cannot find the path specified.”
Even I login on the domain controler as an Administrator who is member of domain admins, enterprise admin, local administrator and group policy creater and ownner.
Can some body tell me what should I do to open the domain security policy ? Many thanks…