Ok, I just downloaded it to check it out.
After unzipping the mod the file should be:
(install location)\Morrowind\Data Files\AreaEffectArrows.esp
install location is where you installed on your system.
If this file is unzipped in this folder, then the launcher should identify it.
With Tribunal installed, you have all the relevant patches. If the Launcher still does not recognize it, I'm stumped.
Maybe you have a corrupted file. Try downloading again from
here and unzip the mod fresh.
Hope this works for you .....
Good luck CV!