Ken, I believe I may know what is causing this problem. When you installed an add-on aircraft (A WestWind CRJ-200LR), the installer for that aircraft overwrote the FS2004 UNINSTAL.EXE with an UNINSTAL.EXE for that aircraft.
The FS2004 UNINSTAL.EXE I have is 4.15 MB in size, last modified 10/12/2004.