Gmaptz.img and gmapbmap.img aren't the type of disk images as Windows thinks they are. You can't open them by double clicking them, and the conclusion (in het error message) of Windows is incorrect.
Also you can't delete the OS of the Montana like you would do on a Windows PC. Erasing all files or formatting the Montana will likely result in a brick.
Scan the Montana with JaVaWa Device Manager for errors. Use it to create an online report of the Montana and place the URL here. The information in the report can help us to give better suggestions.