This is an annoying issue I discovered today. I was trying to download a package but it failed because it wasn’t compatible with my current version of NuGet. So I tried to update the NuGet Package Manager but that also failed. To make things worse still, the NuGet Package Manager uninstall button was disabled so now I was at a complete dead end.
The solution is to run VS2010 as Administrator (right-click the menu item and select Run as administrator)
Go to Tools > Extension Manager, and NuGet Package Manager uninstall button should now be enabled.
Uninstall NuGet and restart VS2010. Then from the Online Gallery, install the latest version of NuGet Package Manager. This time it should be successful.