The NuGet team just released NuGet 1.8. Unfortunately there is an issue when upgrading it via the NuGet package manager. The following message appears and the installation fails.
VSIXInstaller.SignatureMismatchException: The installed version of 'NuGet Package Manager' is signed, but the update version has an invalid signature. Therefore, Extension Manager cannot install the update. at VSIXInstaller.Common.VerifyMatchingExtensionSignatures(IInstalledExtension installedExtension, IInstallableExtension updateExtension) at VSIXInstaller.InstallProgressPage.BeginInstallVSIX(SupportedVSSKU targetAppID)
As explained in the NuGet release notes, one solution is to uninstall NuGet from the VS Extension Gallery before reinstalling. Note: If Visual Studio won’t allow you to uninstall the extension (the Uninstall button is disabled), then you likely need to restart Visual Studio using “Run as Administrator.”