Unknown file type lists as OCTET, cannot manually upload new copies to the site

I have a bunch of non-normal file types for things, one has a .cpnx extension. The site lists this as an OCTET file type. I've tried manually uploading a new copy of a file that already exists, but when I choose the file it says it's not the same file type (even though it's the same file name and extension) and won't let me upload.