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Manage installed package => "Operation failed / Value cannot be null / Parameter name: key"
When I try to manage an installed package on the Solution level, e.g. to add it to another Project, I always get the following message box as soon as I click the "Manage" button:
Value cannot be null.
Parameter name: key
After that, all buttons in the package manager GUI get disabled, including Close, and I can't even close the dialog any more (clicking the "X" button in the title bar has no effect). This means that I have to kill my Visual Studio instance and restart it to continue working.
This means that the only way I can add or remove a package through the GUI is on the Project level.
Visual Studio Premium 2012 11.0.51106.01 Update 1
Windows 7 Professional SP1
EDIT: Attached NuGet.config. Settings are default values.
EDIT2: I never had this issue with Visual Studio 2010.