Can't answer about the gps signal loss (I don't use the garmin XT), but if you want to get it to work, there are a few steps:
1) start the program. Tell it to connect to a Garmin GPS, then have it fail (click skip or whatnot). Then it will run without a GPS signal. You need to go to the settings... About, and write down the device ID (it's a 10-digit number thing). Bring the SD card back to your computer...
2) Head back to your computer. You will need to find an appropriate map (do the usual search -- I'm not posting anything like that here). You will also need to get yourself a copy of "Garmin Unlock Generator" (same sort of place will have it). Every map has a map code (a three-digit code), or is a fully unlocked map.
3) Run the key generator. Select Garmin XT. Give it your device ID, and it will generate a long unlock string. Copy that string down into a file named 'SW.UNL' in your Garmin folder on the SD card.
4) Copy the map to the Garmin directory. Generate a key to unlock said map, and put that in a file named gmapsupp.unl (should match the map file whose name is something like gmapsupp.img??).
That should get you past the unlocking... As for the other problems with the Garmin code, someone else will have to help you...
