Thanks. I used two other antivirus programs to scan T2Fix_1.27b.exe, and they both reported nothing wrong. So, I disabled Webroot, did the install, and everything went smoothly. T2Fix_1.27b found that my original installation (1.25) was bad, so I had to do a fresh install. It is worth noting that T2Fix_1.27b takes care of the complete fresh install by itself, using my software CDs. I did not have to worry about patching to 1.18, etc., the previous procedure.
The only problem I had was that after the fresh install the key bindings file user.bnd was back to default. I had a lot of custom keys that I hated to lose. I was lucky that I had my own good key bindings in my Thief Gold folder. Copying that over fixed it.
You have an excellent piece of software there. Thanks for your help!