I just revisited a problem with viewing or burning a downloaded 5.5 GB ISO file, and the dreaded "CD-ROM is NOT in ISO 9660 format" issue plagued me again.

and I came back to the same solution

AcetoneISO2 !!!!!!!!!!!!!!!!!!

and I was able to copy all the files to a folder, great!!

I hope it helps, it was tough to find a solution