Thank you for your attention to this matter.
Your example seems good to me. I can get my code to work as well, if I remove the chart control. All the other controls (text boxes, buttons, etc) in the Update Panel seem to work just fine. The chart control is rather sophisticated, and has clickable nodes and other client side functionality that complicates the whole environment.
I will post, again the part of the page that is erroring, with the text in yellow that is highlighted in my IDE. It is odd that partial lines are highlighted, so I thought I would reproduce it here, in case that gives any clue as to what the underlying problem is. The yellow text EXACTLY replicates the highlighting that I see in Visual Studio.
<form name="form1" method="post" action="explore.aspx" id="form1">
input type="hidden" name="RadScriptManager1_HiddenField" id="RadScriptManager1_HiddenField" value="" />
input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwULLTE2NzIzMjI4NzcPZBYCAgMPZBYCAgMPFCsAAhQrAAIUKwACDxYCHhdFbmFibGVBamF4U2tpblJlbmRlcmluZ2hkEBYBZhYBFCsAAmRkDxYBZhYBBXNUZWxlcmlrLldlYi5VSS5SYWRUcmVlTm9kZSwgVGVsZXJpay5XZWIuVUksIFZlcnNpb249MjAwOC4xLjUxNS4yMCwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj0xMjFmYWU3ODE2NWJhM2Q0ZGRkGAEFHl9fQ29udHJvbHNSZXF1aXJlUG9zdEJhY2tLZXlfXxYBBQxSYWRUcmVlVmlldzGv38IwaZeoevzvxnflD61GufbRZA==" />
One other odd thing about this...
When the error is thrown, and processing is stopped in the code...
In the line "<form name="form1" method="post"..." where the highlighting starts, if I hover my mouse over "method" then a tooltip appears, and reads "post", just as the code shows. The same thing happens if I hover over "action"...the tooltip matches the code on the page. But, if I hover over "name", instead of the tooltip reading "form1", the tooltip reads "elmnt$orgChart$GoView1" which is the clientID of the chart control. The same is true if I hover over "id".
This is probably a meaningless observation but, I thought I would point it out.