Some years ago when I first updated my TT One with GPS Underground before it closed originally, where I could not use a 4G SDHC with a large map and was suggested at the time to update to Ver 5.5106.
But now it looks if I have same problem with my sons GO500, his boot is Ver 4.86. His 'GO' will not start with a SDHC with the same files as mine with the new ...