title: NuGet upgrade issue
body: <p>I have the version of NuGet that comes with MVC3 (1.0), but when I try to upgrade to the latest version (currently 1.4) it failes and I get this in the log file:</p>
  
  <blockquote>
    <p>6/27/2011 1:25:08 PM - 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)</p>
    
    <p>6/27/2011 1:25:08 PM - Install Error : 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)</p>
    
    <p>6/27/2011 1:26:27 PM - 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)</p>
  </blockquote>
  
  <p>I even tried uninstalling NuGet (via Add or Remove Programs) and installing 1.4 manually, but I inexplicably get the same message. Any idea what I'm doing wrong?</p>