Pascal,
deleted file you suggested (C:\Users\xxx\AppData\Roaming\ptc\.ptcmXXXX), and also deleted the .wf folder (C:\Users\<USERNAME>\AppData\Roaming\PTC\ProENGINEER\Wildfire).
Restarted Creo with the new config file, re-registered with Windchill. Creo then ran fine, with the new config settings and all.
However, upon Creo shutdown and subsequent restart, same issue.
Andri