WRT the Enter key, I meant when you're on the datasheet, not in the form header. Setting it to 'move to next record' should do just that - once you're on the datasheet. However, that may only apply where the focus is given to the datasheet by way of mouse click. In your case, I think the problem would be that setting the focus to the field will select the data, then usual keyboard action won't work until the field is deselected. I wasn't able to work that out by setting the selLength to zero but I came up with this:
Instead of setting the focus in the after update event, use DoCmd.GoToControl "NameOfControl" and arrow key should work then.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.