First of all you make sure you use the latest version of
FairUse4WM At the moment it is v1.3 or 1.3 fix.
You may test Fairuse4wm on demo DRM protected files from fairuse4wm.com and ezdrm.com.
Note that some WM installations will have multiple ECC key-pairs, so you will likely have to "Extract Keys" using multiple licensed files. If you find a file that doesn't convert, try extracting keys wth it. Once your whole set of keys is extracted, you will no longer need to run WM per file.
To remove DRM protection from one-play license files:
If you experience problem using Fairuse4wm, but you have files you could re-download and re-acquire licenses for, you could re-individualize and try Fairuse4wm again. Back up your C:\Documents and Settings\All Users\DRM folder before re-individualizing, in case you need to restore it later.
After you re-individualize, try to unDRM your files first, before acquiring any new licenses. If it doesn't work, then try acquiring new licenses. You could also try dropping the files into the list in Fairuse4wm, right-clicking and getting the key info, and then using that with drm2wmv, but it won't work for me (no private key found for the files).
FairUse4WM: UNABLE TO DECRYPT: Windows Error 80030002 while finding KID in V9 store