I have ran into this same error, With .Net versions above 3.5.

My symptoms were that I'd spawned a new process from a tooltip command, and often, but not always the tooltip message handler would throw the error shown above.

Moving the tooltip command to a button stopped the error from occuring. This I deduce that there is a bug in the ToolTip WndProc procedure that causes this. For users seeing this issue, my recommendation is trying to move your command out of a tooltip and see if this fixes the problem. Only a workaround I know.