FYI, this error message will occur if there are .bt0 files missing in the RealTracks folder (or present, but with an older time stamp than the WMA or WAV file)
Every WMA file needs a BT0 file with tempo stretching information. If it cannot find it (or if it is dated older than the WMA file) , the program tries to make it. So you could have a look in your RealTracks folder, and see if you are missing some bt0 files.
We can make a patch that has those missing files, but first would like to see if/why this was only reported by 2 people.