When I tag mp3 files, Windows Media Player stops working

I have downloaded some mp3 files from youtube. I can play them with Windows Media Player. These files don't have a Title or Artist. I cannot add those in File Explorer, those fields are not editable. I can tag them with MP3TAG. However, when I do that I can not play them with windows media player, I get an error message "Windows Media Player encountered a problem while playing the file." When I look in File Explorer, the title and artist file are still empty. If I remove the tagged fields in MP3TAG, Windows Media Player works again.

Any suggestions?

a) use the suggested tools to check your files for integrity.
b) see here:

There is no download option from YouTube. I believe you have likely used a 3rd party online converter tool. This is the source of the problem for this and several other recently reported issues. See the link posted above for more info.