Hi Mr W, what is the current version of compressor.app you are running? The error is likely caused by residual STATE information use by Qmaster. Regardless of whether you have set up a set of node clusters of not, if you have enabled Qmaster (cluster) in any way or previously, it's likley that the Qmaster network agent of old or in the NEW Compressor.app V4.1 - the new SharingHelperApp is negotiating network (likely Bonjour) paths that are not there. There will be eroors logedon the usual places.
Please post the Version of Compressor.app you are using. The fix is very easy.