Thanks for your reply. I have done all of this. If you read my question - the problem is the following:

MAC users must save the file as a Windows CSV file.

As stated each time our version of Excel does NOT give us this as an option. Therefore every single version of CSV saved is an "invalid file format". This is extremely frustrating and I cannot be the only user with this issue.

Can someone provide me with an actual solution and not just copy and paste responses.