Here is what caused the problems:
I show a map within a messagebox, so the player knows where to go. This messagebox is part of an item where you choose the different running taks. If you close this messagebox everything works like a charm if you don't, there is this slightly chance that the oregon will crash when entering a zone.
Interesting is, that a message shown by a timer -in my case the one that shows the elapsed time- doesn't cause any problems.
As a workarround i force the player to close the messagebox and let him choose the point in the location tab. It wold be nice to show the location screen directly but this is a non working feature.