After loading all the files into Mp3tag, create a snapshot of the Mp3tag status area, which is located at the lower right corner of the Mp3tag application window, and attach the picture to your next message.
As WMP relies on a database in the background it could well be that you have a number of orphans in the WMP database - this applies especially if you have modified files with MP3tag recently.
In WMP up to V10 press F3 to rebuild the database.
Also, it could be that you have accidently apllied a filter in Mp3tag. Check the status bar at the bottom right whether the number of read tracks is higher than the number of displayed ones.
The creation and sending of a graphical screen snapshot relates to the basic skills of computer handling.
Hmm, the simplest way would be pressing the keyboard [Print] key, then use a graphical application to get the print screen picture file from the clipboard into the graphical editor, then draw a selection frame around the relevant data area and crop the selection, then save the remaining picture under filetype JPG or PNG, then attach the picture file to your forum message.
Many graphical applications have a snapshot tool already built in, which allow to set the snapshot area dynamically as needed.
As 'ohrenkino' has pointed out, the difference of counted/loaded files between Mp3tag and the other application can have several reasons.
One reason can be, that the applications have different file read masks.
That means, each application has its own special set of filetypes and filename extensions, which are supported and allowed to be read in.
You should make sure, that both application can read and load the identical file types, otherwise the number of loaded files will differ.
See dialog "Mp3tag/Tools/Options/Tags", group "Tags", edit field "Restrict incoming files to:".
There should be an entry like the following ...
*.aac; *.ape; *.apl; *.asf; *.flac; *.mp+; *.mp1; *.mp2; *.mp3; *.mp4; *.m4a; *.m4b; *.mpc; *.ogg; *.ofr; *.ofs; *.spx; *.tta; *.wma; *.wv; *.tak; *.oga; *.flc; *.m4v;
Another reason could be, that the files in question have different owners, and the applications have different rights to find and read the files.