The Cell End Edit event occurs only when the cell exits edit mode, which it cannot do if it fails validation.
And the Error Text tooltip won't be shown as we described in the 2nd issues. Cell Validating event occurs only when a cell value is changed. In case when Esc is pressed, the value remains the same and no validation is needed. If no text is entered in the these columns the Cell End Edit is not fired, and obviously as you stated, the Cell Validating is not either.
In case when Esc is pressed, the value remains the same and no validation is needed. However, you can handle Cell End Edit event in this case and reset the Error Text property. Even if I click in the cells and click out the Cell End Edit is not fired, so I am unable to update the Error Text.
This displays an error icon with a Tool Tip that contains the error text.
In the Cell End Edit event handler, set the Error Text property on the row to the empty string.
If the cell value fails validation, set the Cancel property of the System. This causes the Data Grid View control to prevent the cursor from leaving the cell.