Your file got somehow corrupted which unfortunately happens quite often with Prime and Prime does not provide any means to cope with that problem (like automatic periodic backups) or any means to repair a corrupted file. So the best you can do is to make backups quite often on a regular basis.
I tried to repair your file but the links to the images got broken. Attached file is in format Prime 6, so you should be able to open it with Prime 7.
Most of the images could be saved, though, and so I attach it in a separate archive (media.zip) and you may embed it in the file again.
Hope it helps.
