@Cabriootje
Hmm, no ideas, only options. Regarding your error message, it looks like your internal storage(in the RNS315)are damaged. Never seen this error message.
Like User
@narum said, if you can send us an screenshot from your setup menu(with Partnumber and Firmware Revision), we can see, if a Firmware Update is possible.
Do you have the option to run Navigation direct from SD-Card(without installation)?
Don't know if your VW dealer has possibilities to reformat internal storage, maybe you will give him a try ?
best regards
Frabusoft