Navigation on my S Class 53 plate car suddenly stops and displays message Navigation Disc not recongnizing or words similar to that effect.Problem seems to be getting worse and I find it hard to understand why now as I have never had any problems before this and it's the same DVD disc that I am using.Going down south on Monday I really need navigation.Any quick ideas,solutions or advice would be very helpfull.

Is the disk an original one or a copy?

If its a copy then try an original disk as they really do work a lot better and prevent the overheating issues that copied disks can cause.

Failing this, try a CD lens cleaning disk. One of the ones that has the brushes on a disk with a small amount of cleaning fluid applied to the brushes.

Thanks,will try that.