a posible cause is an antivirus that refuses permission to write to the drive for not fully trusted programs, to fix this you have to tell the antivirus that terratech ( and the steam and ttsmm(assuming you use it) are trusted programs
It might not be an antivirus you downloaded. It may be your OS’s antivirus. If you play on Windows, you can look up how to change program permissions. A simple (albeit probably not the safest) workaround is to change the program settings to run as administrator.
As far as whether you have a downloaded antivirus, I would look for some common antivirus services on your computer, like McAfee or Norton Security.