If you use SQL Server 2000 on a machine that is running Windows Server 2003 and fail to start a transaction against a linked server because of the following error:
Server: Msg 7391, Level 16, State 1, Line 2
The operation could not be performed because the OLE DB provider 'SQLOLEDB' was unable to begin a distributed transaction. OLE/DB provider returned message: New transaction cannot enlist in the specified transaction coordinator.
you should check whether Data Transaction Coordinator (MS DTC) can access the network. By default, the network access settings of MS DTC are disabled on computers that are running Windows Server 2003.
Follow these steps to enable the network access settings of MS DTC. In my opinion though, it is not necessary to reboot the computer for these changes to take effect.