group policy is not appliying

sir, i m using a windows server 2003sbs as a domain controller from last four months but from last one month, group policy is not applying in any OU.when i m creating any another OU then it behaves same. And another thing an optin “default domain controller policy” is also not opening and a message comes.. “the system can’t find the path specified”. but when i create new policy for new OU it creates easily but policy is not applying on any destination users.. kinly help me…