I had exactly the same problems being described here and after about 8 attempts at trying to patch the system found the following method worked for me.
1. Backup the current working system with Explorer.
2. Delete EVERYTHING from the internal hard drive (not format) so you have a clean system.
3.Log on to HOME and it will download onto the blank hard drive an old navcore (cant remember what it was-8.30 or something and about 33mb)
4. Disconnect TomTom from Home then reconnect again ( I dont know why-I just did it). You will then get offered another newer navcore around 49mb.When this had been installed I mistakenly thought it was 9400 and so I used FastActivate Premium to patch it.
5. Install map 885 (UK & ROI) which auto patches itself.
6. Connect again to Home which then offers 9400 navcore, install it and patch everything again. I cant remember whether I re-booted the device and then patched everything or not so you may have to experiment with variations of the procedure.
7. The down side of the update is Home will not allow install of any start up or shutdown sounds. The TomTom drumbeat and its splash picture work OK. Also I have discovered a minor problem with the new map as it is incorrectly indicating I have arrived at a destination which is about a mile too early but its only one fault and nothing to do with the download. Also I am not keen on the old looking icons in this navcore but they do their job.
System - TT 720
Map 885 UK
Nav 9400
SD card not in use