TomTom One XL Hangs when Western Europe 1GB 900.4608 is added

[Rincewind]

Driving me nuts this one

I have a working TomTom XL with UK + Ireland 900.4608 and USA Canada and Mexico 845.2670

I added Western Europe 1Gb 900.4608 (WE1GB) and TomTom stopped working - it now locks up after the logo and before the page of text with I Agree at the bottom. I can reset, reboot but it continues to lock up at the same point.

I then deleted the WE1GB map from the SD card, rebooted and it still locked up at the same place. The only way to get it to work was to restore all the files from the backup. I presume some files got modified during the boot process and they stayed screwed up.

I checked the maps are OK by loading them on my HTC under WM5 and they works just fine.
I checked the SD card (chkdsk reports its fine)

Any suggestions as to what the problem might be?

TFAI

ttgo.bif reports
DeviceName=TomTom ONE
DeviceVersionHW=ONE XL
RamDiskVersion=20091014
BootLoaderVersion=52914

UPDATE:
I think I have narrowed this down to a Map problem. if an earlier map (e.g. 865.3529 that has worked before) is selected, TomTom shuts down and restarts correctly
The 900.4608 UK map is (as I understand the compatibility chart) OK with One XL (version 8.562) and it certainly works but one time only.
Anyone any offers as to why? In the meanwhile I'll go try .4600