I think this has to do with whether or not the file contains a
MacBinary header. MacView seems to be picky in this repect. These headers
are usually added when a Mac program is uploaded. Some Amiga and IBM
programs expect it to be there, some don't. It's a matter of stripping off
or adding 128 bytes at the beginning of the file.
Unsit doesn't put it in. All appropriate email addresses for the author
are in the readme file.