Thanks for the workaround. Unfortunately I get this error in the log now:
15:43:09: [Interface:OpenJob] Error: TestException
bei NSwarm.FSwarmInterface.OpenJob(FGuid JobGuid) in d:\Perforce2\UE4-Releases\4.5\Engine\Source\Editor\SwarmInterface\DotNET\SwarmInterface.cs:Zeile 2007.
At least the message from the title is gone.