I've had that happen, too - I burn enormous MP3 CD's to play in our CD/DVD/MP3 player in our livingroom. Often with over 100 songs. At one point, however, I was having issues where it would only play the first 70 or so.
I think my problem was one of two things:
1) My burner was dying (which it did and I had it replaced under warranty) - but I wouldn't jump to this conclusion for yourself
2) Another time I realised some of the songs were AAC format - those won't be burned to an MP3 CD. All the songs MUST be in MP3 format.
Dunno if the second one is your problem or not - I know it's easy to miss a few AAC or AIFF formatted songs and have them sneak into a playlist only to have then not even burn. Ugh.