Okay, you didn't say so directly but I'm guessing you don't have a full installation of Mobile PC and instead, you are running the downloadable update as a free trial. If that is the case, the first thing you need is a basemap. I have no idea what sort of behaviour you will see in Mobile PC without a basemap. The only thing I can predict is that it will be unpredictable and probably not consistent.
If you look in the folder that Mobile PC installed itself into, you might see as many as three relevant map files. The installation folder will be
..\GarminMobilePC. The rest of the path will depend on where you told it to install itself. Look in the folder that has the program files and you might see files with any of the following names:
gmapbmap.img -- the basemap
gmapprom.img -- the built-in maps
gmapsupp.img -- the detailed maps you have compiled and transfered from Mapsource.
If there is no basemap, you can get one for testing from
here. Just unzip it and put the basemap (gmapbmap.img) in the GarminMobilePC folder. Ignore the detailed map file in the Zip. It's a topo map of Portland, OR, and won't be of any use to you in your testing.
When you compile and transfer some detailed maps from Mapsource for testing, do
not include any map segments from CN 2009. They are locked and there's no way for you to unlock them in that trial version of Mobile PC. Only include segments from Metroguide Canada because it's not locked ... easiest is to just grab all of Canada and transfer it for your testing.
If there is already a
gmapsupp.img file in the GarminMobilePC folder you can cheerfully ignore it. When you compile and transfer a new one with only Metroguide Canada details in it, the new one will overwrite the old one.
I hope this helps.
...ken...