I provided credentials to NuGet but nuget.exe doesn't know these and fails, the error message is a bit cryptic :
Warning 1 Cannot read keys when either application does not have a console or when console input has been redirected from a file. Try Console.Read. C:\Users\aldion\documents\visual studio 2010\Projects\WebApplication110\WebApplication110\EXEC WebApplication110
Error 2 Unable to find version '2.1.0' of package 'ClassLibrary59'. WebApplication110
Error 3 The command ""C:\Users\aldion\documents\visual studio 2010\Projects\WebApplication110.nuget\nuget.exe" install "C:\Users\aldion\documents\visual studio 2010\Projects\WebApplication110\WebApplication110\packages.config" -source "" -o "C:\Users\aldion\documents\visual studio 2010\Projects\WebApplication110\packages"" exited with code 1. WebApplication110
Another case:
http://nuget.codeplex.com/workitem/1659