As your application grows it depends on external files like libraries, images and data files. Assuming that you build your code from both the desktop and the device, it is very important that the device files and the desktop files are up to date. The solution is to work under Activesync synchronized folder. By doing so, the files will be synchronized between the device and the desktop. If you don't have a synchronized folder, open ActiveSync - Options - Choose to synchronize files.