Yes, after much trial and error, I discovered it was caused by a process named QPService.exe. It is part of HP's "Quick Play" application. If I disabled this process with "Task Manager", Mobile PC searches worked fine. The only way I was able to stop this process permanently was to uninstall the "Quick Play" application. Did not want to just hack the registry.
Garmin's tech support had not seen this behavour, but finally said it must be some other application causing the problem, so I began the search.
We're MUCH better now ...
Brad
I also recommended to Garmin that they add a Truck/RV profile like the new 465T Nuvi to Mobile PC as I found attaching a Laptop to a pedrestian to be some what painful. Quite easy in my Freightliner RV. Here's hoping.