After wasting nearly a week trying unsuccessfully to activate some maps on my Tomtom ONE (and WinCE device) I have discovered - almost by accident - that security software Zemana Antilogger interferes with the activator. If anyone else is having these problems it is worth disabling Zemana temporarily (right-click the icon and enter Capcha code). It also blocks the activation of maps of the "With Installer and Activator" type, and possibly others.

Add an exclusion in Zemana Antilogger for FastActivate.

The trouble is the heuristic engine within the antivirus software.

This looks for code within an app that modifies another file or application, and stops it.
Which is what fast activate does when it patches the ttsystem file.

If you don't want to disable Zemana, tendrivers suggestion works; look in MANAGEMENT CONSOLE > RULES
You won't find FastActivate listed, but the following programs:

tt8_mapcheck2.exe
tt8_keygen2.exe

click Allowed against each of these.

Works for me. Bon chance!