Behavior:
It could be possible, that when editing a workflow with Workflow Designer or just trying to open an already existing workflow an error message appears reporting:
The definition of connectionId threw an exception. ---> System.InvalidCastException: Unable to cast an object of type 'System.Windows.Input.CommandBinding' to 'System.Activities.Presentation.View.DesignerView'.
Solution:
Usually this message is regarding the .NET language pack installed on the computer. Please, check it the Workflow Designer works on another computer and then install the same .NET framework version and the language pack for it. If necessary uninstall other language packs installed on that computer.
The operating system tool LPKSETUP can help to remove language packs, just open it with Start>Run.