Hi,
I just tried creating a restricted user, then logging in as that user and running TopoFusion. It worked just fine. I don't know much about windows security -- it was just the default "restricted" user. Maybe there are other settings for your user(s)?
Also, which OS are you running? I will try to think of what else could be causing it. Write permission in the map directory is a must, also in the TF directory itself for the ini file.