I ran into an issue earlier today where I had a web control inside of an UpdatePanel that was causing some errors. So, I began looking for ways to circumvent removing the UpdatePanel and readding it at a later time. I posted a message out on the ASPAdvice.com lists and received 2 great responses. One was from Mike Campbell who pointed me to the "official" debugging page on AJAX (http://ajax.asp.net/docs/overview/ASPNETAJAXDebuggingAndTracingOverview.aspx). The other was from Wally McClure who pointed out that since the issue was server side, I had two options. First, I could have attached VS.NET to the IIS process on the remote machine (although the machine would have needed Visual Studio Remote Debugging enabled). Or, I could modify the script manager on my site. I opted for the second option. I created a Page_Init event on my master page which is where the script manager is located. I then set the SupportsPartialRendering property to False. This allowed me to see the server side error messages.
Thanks again to both of these guys!