Nav drive issue probably. If you're lucky its just the nav disk. If you've been using a copied disk in there then its probably the drive
Talk to alfie (Mercedes Retrofit Specialist - Comand.co.uk) he can easily diagnose and keeps
a) new drives (and a significant discount to Mercedes RRP)
b) normally a refurbished one in stock too
So that probably gives you an indication that nav drive failures are quite common, often a copied disk and failed firmware upload when the copied disk is installed.