Okay. When you said "few machines", how much exactly? And what kind of OS are they running? Check if the permission of the qubeworker service has been changed to anything else besides system. It should be permission-ed as system.
I suggest try running the worker.exe manually through the command prompt. So in your command prompt cd to C:\Program Files\pfx\qube\sbin, then invoke the worker.exe, and let me know the results.
Also I looked up the win32 error code 1420 means "The window is not a valid dialog window", which does not help at all.