Why does EM CC not add an extension that is valid but claims it is not?

I am trying to load a project 7 Dreamweaver CC extension and EM CC says it is not a valid signature.

I have talked with P7 support - the extension is valid, they can not duplicate this problem or have any reports of others having this problem.

I have had no problem installing other P7 extensions.

Computer is Windows 7. I have also tried running EM CC as admin.

Thanks

Ernie Booth

Raleigh, NC