The RPC server is unavailable
"The RPC server is unavailable" is usually indicative of a problem on the Outlook side of things. Try each of the steps below to fix the issue.
1. Reboot your PC
2. Try syncing with Outlook closed and then try syncing with Outlook open.
3. Trying to sync a large amount of changes made in Outlook can trigger the error. Try the sync again a few minutes later.
4. If you are using Exchange, make sure Cached Exchange mode is turned on.
5. Try disabling any other synchronization software that may be interacting with Outlook such as ACT!/Outlook integration.
7. Within Windows Firewall create an exception for CompanionLink.exe
NOTE: Outlook 2010 64-bit users create an exception for CompanionLink.exe and ClxMapi64.exe
8. Try disabling any anti-virus, or 3rd party firewall applications running on your system.
More info on Windows Firewall: