I have DefTweak as well, and except my famous lost connection bug (still unsolved) everything else works fine.
I've just noticed there is no way to remove default tracks, I guess they're encrypted or something. Those .gcf files.
You can try a fresh install of Race07 if you have the time. Remember to save your setups, TA's etc. Or, you can wait for expert guys - recommended - that might now better.