by Mary Cooch.
Wendi: I suspect the reason you are being told you can only upload CSV files is that you are trying to upload your course via Site administration>Courses>Upload courses -this is actually used for creating courses from nothing using a CSV file (the same as Upload users will add new users to the site)
So you need the "Restore" option - because you have backed up a course as an mbz and now you are going to restore this course to a new site. Have a look at Course restore