Itunes? on windows - we have to help you from this terrible cicumstance.
2 options (2nd option is easiest to disagnose)
Consider trying IO Bits ASC [Advacend System Care] (exceptionally useful even in free mode - dont get caried away with installing all it offer although may of the tools I use from there are good for this purpose not essential),
Reinstall musicbee, ASC will now collect the installation data on ALL files installed, and export a list of everything.
Then run ASC's uninstal option, it will remove everything, anything left can be located using another free app called "Everything" - remove all by hand if necessary.
reinstall a fresh copy of musicbee.
all the above maybe not be necessary it may simply be due to windows 255 character limitation.
Insure your folder & filenames character totals do not exceed 255 characters [a windblows limitation]
if they do then they wont be read, so you'll need to shorten "something" - folder path, folder name or the track title
ie including your C drive + whatever folder name eg Music then thats inside another folder (?)
"Music from the 60's" then inside that is (?)
"The Jim Hendrix Experience Discography"
with another folder titled
"The Jimi Hendrix Experience - whatever the album name (Publisher - catalog number) year 196X (mp3)"
then inside that are the tracks titled :-
"track 01. Jimi Marley Exponentially Experienced beyond Belief
- Oh my what a really long name.mp3"
as you can assume it's already well over 255 characters anmd simply will not be read.
Shortening them will fix that issue - there's other ways but having asytem of foldering with short be concise names works a treat, and provides an already structured means of finding your music within musicbee via computer folder tree etc.
As said to remove all Musicbee's leftovers the free tool (which is far better than windows explorer anyway, called "EVERYTHING" will help you locate... well everything.
PLEASE do not use itunes, yuk, spit.