@Skylinestar
Although a very nice and user-friendly program to use, MapSource is no longer supported by Garmin and is not recommended for creating CNNT images, particularly large ones. The recommended programs to use are BaseCamp & MapInstall. MS compiles img files somewhat differently and because it may create tiny errors in the resultant image, it's just not suitable to use with modern map files. Go to the
[Only registered and activated users can see links. Click Here To Register...] and you'll find plenty of links to help you, even with MS.