Unexpected System.InvalidOperationException: The Visible property cannot be set on Web Part

Question

I am trying to find the cause of the problem described in my previous question where controls on UpdatePanels are not functioning properly. Strangely, this is only happening on intranet clients outside of the main location.

I installed FireBug on a client in the US and clicked on a control. Normally, I would expect a partial update but the response is an error page.

Error An unexpected error has occurred.

Web Parts Maintenance Page: If you have permission, you can use this page to temporarily close Web Parts or remove personal settings. For more information, contact your site administrator. 

Troubleshoot issues with Microsoft SharePoint Foundation. 

Correlation ID: f73a5a93-46c8-40c9-848e-d00395d927ce 

Date and Time: 27/02/2012 15:43:22 

Looking in the logs for the CorrelationID, I found

Unexpected  System.InvalidOperationException: The Visible property cannot be set on Web Part 'g_da16f6e5_a10a_412c_b051_98e67718af81'.  
It can only be set on a standalone Web Part.
    at System.Web.UI.WebControls.WebParts.WebPart.PreRenderRecursiveInternal()
     at System.Web.UI.Control.PreRenderRecursiveInternal()
     at System.Web.UI.Control.PreRenderRecursiveInternal()
     at System.Web.UI.Control.PreRenderRecursiveInternal()
     at System.Web.UI.Control.PreRenderRecursiveInternal()
     at System.Web.UI.Control.PreRenderRecursiveInternal()
     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)  f73a5a93-46c8-40c9-848e-d00395d927ce

Has anyone had this kind of problem before?

What could be causing this (bearing in mind that, in-house, this kind of partial update works fine) ?

Answer 1

Not exactly an answer to your question but just sharing my experience:
My understanding of update panels (and the reason I have stopped using them) is that it sends out an async httpRequest to the same page in background. The server process the whole page (that means all web parts on the page) and sends back the whole page in response and then the panel simply picks up the required html and pastes on the current page without updating the whole page.

I have verified this using fiddler and looking into the response also by attaching debugger on an different web part on my page. The update panel's async request hits the debugger on the other web part also...

So if on the update panel's async request the page encounters error, the server will send back an error page. What this page will be, depends on the customError element in web.config (mode=On/Off/RemoteOnly)