I set up the new NuGet Gallery on a web server (under IIS 7.0) where I work. The site itself is set up and runs fine. We are able to register accounts, confirm email address
In my case it was an old local nuget server. The message I found in the logs:
The schema version of 'YourLib' is incompatible with version 'someVersion.a.b' of NuGet. Please upgrade NuGet to the latest version from http://go.microsoft.com/fwlink/?LinkId=213942.
In my case, I downgraded nuget (downloaded an older nuget.exe) and re-created the package. The push now works. I didn't want to disturb the process elsewhere and I needed a quick solution but of course that depends on the scenario one has. In the long run I will update nuget.