silverlight - WP7 App exits when deployed -

i've been developing wp7 app includes "locate me" style functionality bing maps.

i have prototype wp7 device , can deploy no problem. 2 of collegues have retail wp7 devices , when running app exits @ point.

i assume crash occurs within section of code:

    void updatemap(geoposition<geocoordinate> position, double zoom)     {           _foundlocation = position;         maplocation.center = position.location;         maplocation.zoomlevel = zoom;         txtstatus.text = "found within " + position.location.horizontalaccuracy.tostring(accuracyformat) + " meters";          //display address user         displaylocationaddress(position.location.latitude, position.location.longitude);          //stop watcher if horizontal accuracy high enough requirements converse battery power.         if (watcher != null && watcher.position.location.horizontalaccuracy <= desiredaccuracy)         {             watcher.stop();         }     } 

because message concerning horizontalaccuracy displayed address obtained reverse geocode.

however map goes white (as if start centering on location) , app exits.

both devices work fine when debugging app through visual studio 2010.

all can think whilst connected computer devices using internet connection through usb cable when disconnected using cellular data. can't think why make exit.

as both work whilst debugging how can proceed track down problem?

update

i've implemented global error handling suggested , getting following error: credentials either invalid or unspecified on 2 devices aren't working. mentioned above when deployed, not when running through visual studio.

do have global exception handler, @ least ui thread? might want include 1 shows polite error message in release build, , details of exception debug builds.

that won't for:

• exceptions thrown on other threads
• unrecoverable exceptions such stack overflow errors

if launch vs2010 without debugging - it's still using usb connection - still crash?