WhatIWantMost ASP.NET AJAX RTM broke my UpdatePanel

A few days ago I noticed that something was amiss with the My Wishlist page of the WhatIWantMost.com site. At the time I was working on something else so I ignored it and I returned this evening to take a closer look.

I have these floating divs that are displayed for adding/editing items in your wishlist. All the functionality for showing and hiding them is done server side, but through the magic of the UpdatePanel it’s all done in with AJAX. I didn’t know if the UpdatePanel would work because of all the things I had going on with that page, but it did and I was happy.

Well at least it worked for a while. After my upgrade to ASP.NET AJAX RTM it no longer works completely. The Add Item button still works and it calls all the proper validators and will perform its other proper duties. The cancel button, however, is now broken. The cancel button works simply enough, the onclick event is handled in the code behind and simply sets the visibility of the div to false. This would normally require a postback, but the UpdatePanel catches all those things and does it via AJAX instead.

Now rather than the magic I was used to I see the following when clicking that cancel linkbutton:

A Google search for the term “Sys.ArgumentNullException” has turned up nothing yet other than a mention of that sometimes occurring when using a datagrid, but I am not using a datagrid or any kind of data control in this case.

I suppose its not that big of a deal I can change that Cancel link to work client side since all it does is hide the div, but the point is that it used to work and now it doesn’t.