Trying to load my music library to my old IPOd touch. Some tracks appear "greyed-out" and do not play. Solution much appreciated

I want to utilise an oldish IPod touch (4th generation, 32 Gb) as an MP3 player. I am trying to load my music library in ITunes to the iPod. No matter what I try, some tracks will not load and don't appear in the IPod. Some tracks appear "greyed-out" and will not play. I have tried resetting the IPod, rebooting my IMac, etc, etc. Also tried turning off the automatic music download, but still no joy.

Solutions gratefully received.