Sounds like you have put a mode1 disc in a mk3 mate, you need a mode2/form1 update disc, with some luck you will be able to get your nav computer back, but don't hold your breath.

Good luck.

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.