MPC Beats is not loading all sounds to my tracks

I have been using MPC Beats to start projects and recently have been listening down to a few tracks and noticed that it keeps telling me that some sounds are no longer there. I do I retrieve those sounds to my tracks? I've already save it as a project and still keep losing the information. HELP! Starting to get very frustrated.

This specific tracks have been done weeks ago. I don't understand why now after saving it as a project,listening to these tracks before,several times and now it's randomly not loading my sounds? How do I stop it from happening? How do I get my sounds back?