cant change date n time

hello to all
few days back i joined one of my computer to domain and again after some time i changed it to member of a workgroup, since then i m not being able to change the date and time. whenever i tried to do so i get a msg "You donot have administrative privileges to change date and time even when i logged on with administrative rights. could someone tell me whats the problem and what is the solution for this?

Thank you.