Hey @mcascone, my previous comment was slightly incorrect - my testing showed that ProGet requires the first file in a Debian package to be debian-binary
(see this commit I made in a project a while back).
It looks like you're able to verify such is the case on a Debian archive by running the following on a Linux system:
ar tf name-of-package.deb
And the first line in the output should be debian-binary
.