samples not found

Whenever I load up MainStage 2 and I try to open the grand piano sample I get this error message:

EXS24 instrument "Steinway Piano.exs":

Audio file "Stw ped v1 024.aif" not found!

I have the same for EXS Strings 2, Liverpool Bass, Mixed Choir, Marimba, and something called 1.7 Blue Plate

How can I fix this? Can someone help me? Thanks in advance!