Hey Natalie,

That parser error usually happens when the server returns something unexpected during an asynchronous postback — for example, when exporting or streaming a file like Word from within an UpdatePanel or a control that uses AJAX (like the WebTab).

Since WebTab uses partial-page rendering, the response it sends back isn’t the plain binary stream Word expects — so the browser throws a PageRequestManagerParserErrorException.

You can try handling the export on a separate page or HTTP handler instead of directly inside the tab’s callback. Another option is to disable AJAX temporarily for that specific button click (by setting UseSubmitBehavior="true" or using a normal postback) so the full response with the Word content can be sent.

It’s a common issue with file downloads in AJAX environments — jQuery tabs don’t usually trigger partial postbacks, which is probably why it works fine there.

Hope that points you in the right direction!