Windows Media Player won’t add 1 file to the library

Hey everyone,
I put almost all my music into one folder, and whenever I play a file that I have never played before, it automatically adds itself to my library in Windows Media Player, and sorts itself out as per its tags.
However there is this one song that just won’t add itself. And I can’t figure out how to manually add it either.
It’s just a dubstep song converted from YouTube, I have about 150+ songs done this way, they’ve ALL worked in the past. They’re part of a compilation album that is being continuously added to, it’s called “Monstercat Media 005 – Future”. I have 4 tracks in there no problem. Then the 5th one just doesn’t want to be added!
I made sure the album and artist was exactly the same, to no avail!
They add in iTunes just fine (however that’s because you have to manually add new items into that)
Can anyone help me?
Image to help illustrate issue:
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Answer #1
Sounds really weird that a song you ripped from youtube doesnt add… did you accidentally convert it to a format wmp doesnt support? try copying the song to some random folder and add it to the library..
Answer #2
proximo19 replied: Sounds really weird that a song you ripped from youtube doesnt add... did you accidentally convert it to a format wmp doesnt support? try copying the song to some random folder and add it to the library..
Well, that worked.
I kinda want it in that folder though .
EDIT: Spoke too soon. I restarted WMP, now it’s gone!
Answer #3
Strange, might want to consider this (though it feels like an overkill):

I suggest you to perform system file checker, it scans system files and replaces incorrect versions of the system files by using the correct versions.
 
Here are the steps:
 
1. Click Start, click All Programs, click Accessories, right-click Command Prompt, and select Run as Administrator.
2. Click Continue or supply Administrator credentials if prompted.
3. In the Command Prompt window type the following, and press Enter:
sfc /scannow
Here is an article that will give you information on SFC Scan:
http://support.microsoft.com/kb/936212
Follow these steps and check if it works fine.
1. Close Microsoft Media Player for at least 30 seconds
2. Click Start and then Run
3. Type the following into the textbox:
[list]%userprofile%\Local Settings\Application Data\Microsoft\Media Player
4. Click OK and a folder showing you your library files will appear
5. Erase all the files that end with .wmdb
6. Open Microsoft Media Player
7. Push F3
8. Select the locations for your music files
9. WMP will reindex your music
For more information, logon to:
http://windows.microsoft.com/en-US/windows7/products/features/windows-media-player-12
http://windows.microsoft.com/en-us/windows7/Libraries-frequently-asked-questions
Found over at:
http://answers.microsoft.com/en-us/windows/forum/windows_7-sound/windows-7-windows-media-player-12-wont-update-the/e68d4e33-897c-421d-8d4b-dbf53c9ee4a5
Answer #4
Thanks for your help, I did something found through the link (but not the quoted solution)
I did:
If all these steps suggested above doesnt work close WMP12 stop all running services and try to open : "C:\Users\"Your Username" \AppData\Local\Microsoft\Media Player" and delete all the contained files (maybe copy them to another folder for a backup).
Afterwards open WMP 12 press F3 and the library index works how it is supposed to!