I've been having problems with this error for a while and finally got it solved.
What we have is a form with a number of datagrids which contain combobox columns bound to enums, which was throwing the error when the form is first opened. We discovered that the enum binding must be set before the datagrid bindings are set on the form or else the error will occur. In our case we were setting a property on the form before showing it then trying to bind the enums.
The solution was to bind the enums to the datagridcolumns before setting any other properties on the form. To be sure we also set the enum bindings again on the form_load method.
Another bug in .Net meant that the error was also displayed when we closed the form if the datagrid was not populated, so we set the enum bindings again in the form_closing event, and it all seems to work fine now, thnakfully.
Note this error only seems to appear if we allow the add rows property of the datagrid.
