We are having an unusual issue with Active Directory. Intermittently users are receiving an invalid password dialog when attempting to authenticate. I have verified that the users are not typing in the wrong password or any of the basic mistakes that are made. The accounts are not locked out when this occurs and all DC's and GC's are available when this issue occurs. There are no errors in the event log as it is clean mosting informational events and no warnings or errors. Any help would be appreciated.