This should probably be a FAQ somewhere.
If I remember correctly, this shows up when the find results data gets corrupted, or ends up with specific non-printing characters in it. Usually, this happens when searching binary files.
You can fix it by exiting MEW, and nuking the temporary files containing your search results. Obviously, this will delete the data in the results window, as well.
Check <MEW>\Config\Tmp for a file named MeFind0.tmp or MeFind1.tmp (because there are two sets of results) and remove it. The directory path may be slightly different, but it should be under your MEW install directory somewhere.