OK, let me see
1. Navcore updated from CAB file as supplied doing overwrite... DONE
2. TTsystem and model files copied to root in TT... DONE
3. Use FA 1.8.8.7 + D/L meta to patch additional map stored in SDHC... DONE with no issues
4. Reboot... all good, loads my pre-existing map OK.
5. Try switch to map on SDHC... TT FREEZES.
Any ideas or I'm being just too thick..?