RPC Server Unavailable

Have 4 Windows Server 2003 SP2 machines all recently upgraded from SQL 2000 to SQL 2005. Can connect to SSIS on 3 out of 4. Can connect using WMI to 3 out of 4. 2 of 4 are exactly the same, one being the source and one the target in a disaster recovery situation. Of these two the one that can be connected to with WMI and SSIS is the target, but the source will not work. Keep getting “Win32: The RPC Server is Unavailable” message. Event log on target shows “DCOM was unable to communicate with the computerusing any of the configrued protocols.” SSIS just says “Access is Denied.” DNS appears to be fine. Permissions, services, etc. all seem to be fine. Checked all DCOM settings, etc. between the 4 machines and they appear to all be the same, yet can’t connect to the one machine. Any insight would be appreciated!