Adam,

I worked all morning to make a "Simple" page to do what I described in the previous post - by trying to duplicate the error by placing each GridView/DetailsView set in it's own updatepanel.

It now seems to be working properly though!  The main difference between the "Simplified" version and the one I had trouble with, is that the page that came up with the error used a master page.  I am not sure if that is the problem yet though.  There is so much to keep track of in the aspx code that I need to go over it in very fine detail again to see if I can determine the cause. I will come back with my findings when done. At least I have discovered the value of those expand/contract (+,-)markers in the margin to help visualize specific sections of code.

Anyway, it at least looks like there is no problem when not using MasterPages.  We'll see if that's the problem...

 

PS

  There still is a problem with the DetailsViews controls in design mode showing "There was an error rendering rhe control. Exception has been thrown by the target of an invocation.  But they do function properly.