I have looked up this error code and everything points to issues with the GAL. In the ESM, there is a mailbox that doesn't have a network user anymore. When I go to right click on the name, after 2 mins I get this same error. error 0xc007054b Domain not valid.
I am not able to create any new Mailbox either. When try to create a new user in AD it tells me it can't verify uniqueness of name because the GAL can't be reached.
Global Catalog IS checked on the DC for NTDS properties. However this is an alias name of 21CE9160-7378-4A3C-B3D1-B0713FDD3391._msdcs.(domain name). This name is NOT pingable.