It sounds like the Latitude value that you're passing to GetMap is incorrect. Can you confirm what UserLat and UserLon are? Where are you setting these in your app?
I would suggest that you add a label to your screen and set Text property to your formula.
When you run your app, the label should show the actual arguments that you're passing to the GetMap function. This should help you diagnose the problem, or you could post the result here if you're still stuck.
Tried your suggestion, but the error still exist. Anyway is there any better way to embed imagemap in the app instead used my previous code?