When the GridView loses its focus, the ActionOnLostFocus is "CommitEdit" by default. When the cell is invalid then it cannot be committed.
So if you try to move the focus, you can only if there are no errors. Otherwise the cell is still in edit mode with an error message. Do I understand right, that this is the problem that you have?
If so, you could set this ActionOnLostFocus to "CancelEdit". That way you will be able to move the focus when the cell value is not valid.
the Telerik team
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