There are several things you can check.
1. Make sure your device has been updated to the latest version of app.
2. Check to make sure you have uploaded a RMGC file and not a backup or GEDCOM file.
3. If there is some corruption in your RootsMagic database it may cause the app to not work with it. You will want to run the Database Tools (File, Tools) all options in consecutive order on your RootsMagic database prior to uploading the file to your device.