Unable to connect to the remote connector

After upgrading, our NuGet connector no longer functions. When browsing the feed on ProGet it reports, "Unable to connect to the remote server". I also deleted the feed and re-created it using the default connector and settings (http://www.nuget.org/api/v2/). We are behind a proxy and the proxy settings are configured and test successfully when targeting https://www.nuget.org and http://www.nuget.org.

We can access NuGet directly through the proxy just fine.

Thanks,
Andy

Product: ProGet
Version: 3.7.1

What version did you upgrade from? We haven't changed anything related to proxying in a very long time.

I believe it was 3.5.6...

Is there any way I can turn on more verbose logging to find out what the underlying error message is? This is a pretty big show stopper...

Are you using manually entered proxy settings or Windows proxy settings?

Manually entered:

Proxy Host/Server: value entered
Port: value entered
User Name: (blank)
Password: (blank)
Excluded URLS: (blank)
Bypass Local Address: unchecked

Testing URL: https://www.nuget.org: Success!

The server itself has a Group Policy enforced System/IE proxy setting that is set to a black hole (intentionally).

We've identified what may cause this. On the proxy configuration page, can you enter a dummy value into "Exclude URLs" section, e.g. "example.org"?

Once you save, let us know if that workaround resolves it, and if so, we can fix that for the next version so a dummy value isn't required.

Yes! That worked! Thank you!

Another thing we noticed is that if we are accessing ProGet over HTTP but the connector uses HTTPS, we get a 503 response when trying to use the ProGet feed. Switching the connector to also use HTTP fixes the problem, but it's not ideal.

No problem! Now for a barrage of questions...

Where is the 503 response coming from, ProGet or the proxy server? Is there an error message in addition to the status code? What do you mean by "use the ProGet feed", does that mean browsing the ProGet web application (i.e. feed overview page), or accessing packages via nuget.exe/Visual Studio? And does it work as expected if you access ProGet over HTTPS?