When you use Dssite.msc (Active Directory Sites and Services) to force replication between two domain controllers in the same site, you receive:

The RPC Server is too busy.

If the time on one of the domain controllers is greater than or equal to 5 minutes different from the other domain controller, you will experience this behavior.

To fix the problem, synchronize the time on the two domain controllers.

NOTE: See the following:

How do I configure an authoritative time server in Windows 2000?

How do I make my PDC emulator an authoritative time server for my domain without it synchronizing with a reliable time source?

How does NET TIME determine the Time Source Server?

How do I configure the Windows 2000 time service to log when time is adjusted?

Windows 2000 registry entries for the W32Time service.