nuget error: the path for the selected source could not be resolved

Finally!... the answer!

The problem was running visual studio as administrator.

The network share nuget was trying to access required my own user credentials, but running visual studio as administrator uses the local administrator credentials which didn't have access to the share.

There are a few ways to prevent VS from running as administrator (ex: if you're using a shortcut you need to go to properties and uncheck "run as administrator"), but since I had ran the compatibility troubleshooter on devenv.exe to force it to always run as admin, I didn't know how to undo it. This link shows you how to do that:

https://superuser.com/a/547846/213179

Note: to see other reasons why not to run visual studio as administrator, read the posted question in the above link:

"For those interested, the reason I want to go back is because some features (such as drag-and-drop files into VS, open files from Windows Explorer, etc.) no longer work."

Package Source must be given as wrong path. Try this

• Go to references
• Right and Click on Manage Nu-get Packages
• On the top right you will see Package Source
• Package Source drop down will have a settings button over there
• Remove available packages
• In Machine wide package, tick Microsoft and .Net
• Remove available source package if the directory does not exist