Hi Manolo,
Thanks for contacting Syncfusion Support.
Query 1: When a grid has not data, the program breaks?
By analyzing your application, we found that 4th control’s name is set as an empty string. In ExportAll method, you have assigned the control’s name as worksheet name. As an empty string is assigned here, the exception is thrown. This is a usage level issue.
Query 2: If I set an update panel, it doesn't work.
If you render the control within the Update Panel, it caused an asynchronous postback. So, please use the “PostBackTrigger” to perform post back for the control in update panel. Please refer the below links to know about update panel.
Regards,
Saravanan A.