The EventMoveArgs has a property called Data, which the intellisense indicates if for custom data. I need to pass an additional parameter other than the traditional Id, NewStart and NewEnd with the Callback to OnEventMove. How can I do this?
e.Data holds custom data sent from the client side when invoking the EventMove event manually using .eventMoveCallBack().
If you want to store custom data with the event, you should use DataTagFields to specify the db fields to be loaded and passed with the event.
See here - section 4. Custom Event Data (Tags):