Our Domain controller seems to have some replication issues.
I've inherited this domain & my daily work with windows domains is very limited.
We have one DC & the rest are showing as Global Catalogs.
For some reason the DC itself has 2 names in the active directory (1. "Backup" - this is the real "computer name" & it's listed as DC on the active directory. 2. "DC" - I'm not sure where this name is configured on the server itself but if you look at our DNS server this name is marked as "Static". this name is listed as a GC at the AD).
If I ran the command repadmin /showrepl at any of the GCs you get this message regarding this "DC": "The target principal name is incorrect".