Just a guess here, but that may be because MGE is installed in a directory that is unexpected. Where is your Morrowind installed and where is MGEXE installed?
morrowind is installed in my STEAM folder in my program files. And the only thing with MGE says a folder called mge3, which is inside the morrowind folder.
it contains only something named "No Read-Only" and "MGE XE Default Statics Classifiers.ovr.
when i search for MGE, only MGE XE stuff comes up.
EDIT: ive found MGE stuff. I went to MGSOO>Options>MGE_MO.
Theres 5 things with MGE.
MGE_3_0b
MGE_178
MGE_MO
MGE_MO_NF
MGE_NO
and the MGE_XE
EDIT2: i just tried to open up MGEgui (like the video guide says on step 22. and i get a message saying ive to install MGE to the morrowind directory.