You might try renaming the extension to “cpr.” We sometimes shuttle sessions back and forth between Nuendo and Cubase here, but mostly the other way (Cubase to Nuendo).
Using the Nuendo demo might help - or you send those files to someone who can convert. Maybe it is possible without transfering the audio… I have a system with Nuendo4 - if nothing helps I can open the nprs there and save as cprs… these should work fine in C Elements7…