If a profiled app encounters errors it will log these to the profiler.log file. By default you will find this in C:WindowsTempEQATECProfilerLogs. Try to see if it holds some clues. You can also try to enable "Full logging" in the app options, which will at least output something to the log.
A profiled app is actually the "server" when talking to the profiler; it is the profiler that connects to the app, not the other way around. In your case it seems that the old app has stopped listening (otherwise the profiler s attempt to connect would simply be served by the old app), but the new app has not (could not?) started listening.
It seems strange, though, so my best suggestion is to examine the log-file. It will e.g. show if the app could not start its control-server and if so, why not.