When you change the password policy in your domain, the changes are NOT applied?
If you didn't apply the policy changes to the Default Domain Group Policy, this problem will occur.
If Block Policy inheritance is enabled on the Domain Controllers organizational unit, the password policy will NOT be applied.
To check for Block Policy inheritance:
1. Open the Active Directory Users and Computers snap-in.
2. Right click the Domain Controllers organizational unit and press Properties.
3. Select the Group Policy tab.
4. If the Block Policy inheritance box is checked, clear it.
5. If you cleared the Block Policy inheritance box, run secedit /refreshpolicy machine_policy /enforce on each domain controller.
NOTE: If you didn't set the password policy in the Default Domain policy, configure the password policy before running step 5.