Visual Studio 2010 nuget error: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel

• Go to VS2010 → Tools → Library Package Manager → Package Manager Settings.

• Choose Package Manager → Package Sources.

• Add a new package source as:

  • Name: NugetSource

  • Source: http://packages.nuget.org/v1/FeedService.svc/

• Move Up the newly added package source to first position.

• UnCheck existing "Nuget official package source"

• Restart VS2010.

Go to https://nuget.org/ and get its certificate.

For example, if you're using Firefox: after opening nuget site - click site's icon on the left side of address bar, click 'More Information', and on the Security tab there should be 'Web-site identity' section with 'View certificate' button. Click there, in the opened dialog select Details tab - there you should see chain for *.nuget.org. Click button 'Export' at the bottom and save certificate to the file (add .cer extension manually, because dialog won't do it for you).

Now you need to setup you system so that it will trust the certificate. Press Win+R (Run dialog will be opened) -> type mmc there and run it (with admin privileges if you have UAC turned on). There select File -> Add or remove snapin... -> select Certificates on the left, in the dialog select Computer account and Local computer. Click OK - the tree will have Certificates node in the Console root. Open it and file folder Trusted People. From its context menu select All tasks -> Import... -> Select file that you have exported before and import it.

Everything should be working fine.

We had the same issue in work, and we resolved this by dropping the secure socket, Https -> http. This means you can use the V2 URL http://nuget.org/api/v2/.

Possibly an issue getting rid of the secure socket, but the above URL (http://packages.nuget.org/v1/FeedService.svc/) is also unsecure.