You're missing one of the 'audio' (.wav) files. Are you just sending the .RPP file? It's probably still in your project folder.
Anything you record (or any loops, whatever) you use will have to be sent along with the .RPP.
Be sure to use the same VSTs on both ends of the project.
The project will 'grow' in size rather quickly as you add new parts. Might be easier to use one of the 'free' upload sites (DropBox comes to mind).
You can 'zip' the files to reduce the size. Have fun!
