parallel toolbox createJob is super slow

Hi, I have Matlab 2013a installed with the parallel computing toolbox. When matlabpool is executed it takes about an hour until all 4 workers are ready. Currently I run the validation in the cluster profile manager. This is the current status. Since about 30minutes unchanged:

VALIDATION DETAILS
Profile: local
Scheduler Type: Local

Stage: Cluster connection test (parcluster)
Status: Passed
Description:Validation Passed
Command Line Output:(none)
Error Report:(none)
Debug Log:(none)

Stage: Job test (createJob)
Status: Running
Description:Validation Running
Command Line Output:(none)
Error Report:(none)
Debug Log:(none)
...

The antivirus software (sophos) is deactivated, the firewall is also inactive. Matlab does not consume any CPU power and memory is not increasing either. After the first matlabpool execution, I closed it and ran matlabpool again, with the result that it was starting much faster. Now with a restarted Matlab its slow again.

Where could this extreme delay come from? Is there anything else that I could check?