Reply to issue with finding tracks in traktor?!

Hi all

I don't believe this has been asked before but I'm having a problem with traktor pro s4.

Basically I have 5,000 tracks and I'd say 25percent of them aren't showing up when I browse for them. The folder is there but there's nothing in them. When I open up Itunes, there they are. But they won't work with traktor..

anyone have any problems with this before? I believe there mp3s, they could be a different format but does that make a difference? thanks guys