Richard
I had a similar issue and resolved it by firstly doing as you have said and removing all the language and help files and other shit I don't need then I cleared all my favourites off the device ( I have them stored separately ) and routes etc then loaded the new maps on no problem
Then just re add your favourites and routes etc
Also if you use finder on the mac try sending all the existing maps to trash before you install the new ones
I had a similar issue and resolved it by firstly doing as you have said and removing all the language and help files and other shit I don't need then I cleared all my favourites off the device ( I have them stored separately ) and routes etc then loaded the new maps on no problem
Then just re add your favourites and routes etc
Also if you use finder on the mac try sending all the existing maps to trash before you install the new ones

