I have examined the page and the user control that you have attached in the other thread that you have opened with the same question and I have noticed that you have multiple RadAjaxManager controls, which is not supported scenario.
Please note that when you have a RadAjaxManager on a page, in the user control you must use RadAjaxManagerProxy and not RadAjaxManager. Detailed information on this could be found at the following help articles:
Please try changing the RadAjaxManager in your user control with RadAjaxManagerProxy and see if the cancel issue will be resolved on your end too.
As for the validation, with your current settings, every postback within the user control will force the validation. For allowing the grid to perform operations without the validation, what I could suggest is that you use ValidationGroup
for the TextBox, RequiredFieldValidator and RadButton (Inserir/Alterar).
Hope that helps.
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