NuGet - Installing Individual Packages reporting “The remote server returned an error: (404) Not Found.”

Question

When using a local NuGet server, whenever I try to install an individual package from that server, all I get is this error: "The remote server returned an error: (404) Not Found."

The packages are all there in the filesystem and the feed itself sees all the packages appropriately. I can even browse the package directly!

What am I missing?

I did just upgrade from NuGet server 1.4 to 1.5, but I've seen this happen before. Touching the package files used to help, but that does not appear to be the case now.

EDIT: Actually, I hadn't seen that exact error before...I've seen this one, intermittently, that touching the package tended to fix.