I am having the exact same issue.
It all worked fine with RC1 before upgrading to RTM.
However, after doing a lot of testing, I have found out that all of my update panels work fine if I don't login to my website using the asp.net Login Control. As soon as I log though, some of my update panels quit working. But what I don't get is that some of the update panels don't work, but others do??? Even though they are almost identical? If I log back out, then the update panels start working again?
Some of the errors I am getting are
sys.WebForms.PageRequestManagerParserErrorException: The Message received from the server could not be parsed. Common causes
for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.
Details: Error parsing near '/div>
|html
<head>
'.
AND
sys.WebForms.PageRequestManagerParserErrorException: The Message received from the server could not be parsed. Common causes
for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled.
Details: Error parsing near '/ble>
|html
<head>
'.
So there is a pattern to the errors to? I have did searches to see if I have any Response.Writes and I can't find any.