Hopefully that fix it.
You would have to dig more in the composer logs and look for entries similars to the ones in the KB.
2012-02-24 02:21:27,631 | 3 | INFO | ServiceCore.LockManager.LockManager - Multiple lock are required for SimClone with ids: ad37e069-7f18-4bc6-9b4a-9eec98fdc8b6
2012-02-24 02:21:27,662 | WFE thread 9 | INFO | ServiceCore.WorkflowEngine.CreateSingleCloneTask - Action VMware.Sim.ServiceCore.Action.ReplicationAction40 failed. Task 7bbf7438-9532-47e8-8209-7f253da62dc8 finished in Failed state.
2012-02-24 02:21:27,662 | WFE thread 9 | INFO | ServiceCore.Exception.SimServiceException - Datastore used by VM vm-6223 is inaccessible.VC URL: https://dmvc.aric.com:443/sdk, Username: ari_nt\vcenter.
This is the issue that is known. The problem accessing the snapshot or the lack of dvs ports.
Otherwise check the logs for clues.
http://kb.vmware.com/kb/1027744
Cheers