Info On Invalid Files

I have some old cpr files which I think where made when I had cubase SX. For some reason now they have no name extension and appear as small black boxes with exec written in the left hand corner.I have tried changing the extension to .cpr but they refuse to open saying “invalid file” I have moved the files to another hardrive over the years but its always been within the mac system.
Its not that I really use these files but Im intrigued why this has happened. If any moderators can throw any light on the subject I would be grateful. Im using 6.5 on imac

Are you sure, these are CPR files? You know, the extension may be any, but the header of file is important.

Hi Yes they where cpr files -certainly not midi as I saved them as song files. What is strange is the the file extentions are no longer there…