iTunes will not add some mp3 files

I own several albums from the same band and want to import all of the .mp3 files into iTunes (v. 12.0.1.26). However, iTunes will not add a few songs from 3 of the albums. All of the other songs were imported without a problem except for these few.

I have tried using "Automatically Add to iTunes" in Finder as well as "Add to Library..." in iTunes for these files. When attempting the former, the files are placed in the "Not Added" sub-folder. With the latter, nothing happens (I check by going to My Music => Songs and sort by Date Added to see if any new files show up regardless of expected ID3 information).

The problem files play normally with Quicktime and VLC player.

My Mac is caught up on all software updates.

Thank you in advance for your support!