Unsupported Tracks are found in playlist(s)

I am trying to create a library, but on ejecting I get the message (Unsupported Tracks are found in playlist(s)) I have deleted all M4A files so only have MP3 but that hasn't worked.

I assume that somewhere there are one or two corrupted files that are ruining the situation. But in 2050 files it will be a long process to find them.

Is there any way to find these files?

In the last year I have only bought MP3 files or downloaded WAV files that have been sent to me legitimately, yet I did not have this problem before.

Please help I have wasted so much time trying to resolve this issue.