I have a TomTom One XL and have just gone to upgrade from Navcore 7 to Navcore 8.396 by using one from the sticky thread for WORK/TRUCK (DSA). On the instructions it says
Add the missing "skin" files from the Home DLL folder : all files with "data" in the filename are to be copied to the root of the device.(This is to prevent the errors with the menu or missing/double icons)