Post back after data extract from sharepoint

This is the problem which many of sharepoint designer usualy can't solve,
once you click the “Export” button once, other controls will become unresponsive since WSS post-back will not work. You cannot export another copy neither. The following property assignment of the “Export” button is required for other post-back to work (including the “Export” button itself)

So you have to just provide a OnClientClick property of the button, See below..

oBtn_Export.OnClientClick = “_spFormOnSubmitCalled = false;_spSuppressFormOnSubmitWrapper=true;”;