PDC offline-Can’t authenticate to Domain

When our PDC is offline, our users are unable to authenticate to the domain.

Event viwer shows successfull sync between BDC and PDC.

There are 2 BDC’s on two seperate subnets.

Netlogon running on both. Both can ping PDC by name.

I’ve seen many articles on this issue, but none that have pointed to the right cause.

Your input is appreciated.

GSM