Ошибка из-за невозможности найти элемент управления с автоматически созданным идентификатором '<var>X</var>' для генерации события обратной передачи. Для устранения ошибки явно задайте свойства ID для элементов управления, генерирующих события обратной передачи.

Message in Russian (Русский)

Unlocalized message

An error has occurred because a control with id '<var>X</var>' could not be located or a different control is assigned to the same ID after postback. If the ID is not assigned, explicitly set the ID property of controls that raise postback events to avoid this error.

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