Error: Failed to determine DCs for domains in the forest. Reason for error: Unable to get domains in forest for [ad-igh.nl] - error code 
Trace: at KVS.EnterpriseVault.ExchangePolicySync.ExchangePolicySynchronization.InitializeDomainControllerCache()
at KVS.EnterpriseVault.ExchangePolicySync.ExchangePolicySynchronization.RunSynchronization(ExchangePolicySyncTaskEntry taskEntry, CheckControlEventsDelegate checkControlEvents, Boolean reportMode)
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Most intersystem communication seemt to work and I'm not experienced on RPC issues..
I've ran the commands indicated in support document 340938 and these are the results.
I did not get the error messages mentioned in the support document. as you can see
C:\Program Files\Support Tools>rpcping -s w2k3dc01
Completed 1 calls in 1 ms
1000 T/S or 1.000 ms/T