Unable to access nuget feed from Visual Studio

I can access all features within the web interface for Proget, and have uploaded all the required packages, however I am unable to access the public feed. I have tried using the default Admin account, a second user account with read only permissions, and assigning the Anonymous user to have access. None of these work, the Visual studio prompt asks for a username and password, but fails to authenticate at any time.

It states "Could not connect to the feed specified at ..... Please verify that the package source (located in the Package manager Settings) is valid and ensure your network connectivity.

I know the source is valid as can access it from the web interface and I am copying the feed url directly from the web interface.

When accessing the url from a web browser it shows the following.

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<service xmlns="http://www.w3.org/2007/app">
<workspace>
<title xmlns="http://www.w3.org/2005/Atom">Default</title>
<collection href="Packages">
<title xmlns="http://www.w3.org/2005/Atom">Packages</title>
</collection>
</workspace>
</service>

Any help greatly appreciated.

Product: ProGet
Version: 3.8.6

Hi Matt, I would suggest to attach fiddler, and see what's going on.

That XML you pasted is what a NuGet endpoint looks like; from there you can append /Packages to the URL, and see more of the exposed API.