Further to my original post:
I had installed TMG v8 on an individual's account on a multi-user PC. Although the error noted previously appeared when run from the shortcut, the program worked fine when "run as administrator". The drawback though was that the administrator account became the default account for file storage.
I uninstalled and installed the program through the Administrator account, but needed to select "run as administrator" to run the setup file. I installed it for all users and this seemed now to have fixed the problem. The user can now run the program from his personal account and the default file location is now the user's.