I was working on a site for a client today and needed to open up the default.aspx in SharePoint Designer. I checked out the page and double clicked to open it and was present with the normal option, Edit the Page Layout or Edit in Browser. I went ahead and clicked to edit the page layout and out of the blue was presented with the error The Server could not complete your Request. I tried several different things, tried connect to another site, tried closing SharePoint design and re-opening it, I tried detaching the site from the page layout, no matter what I tried I continued to get the error.
Finally I gave up and went to Google. In a discussing board I found people that were having the same problem and as equally puzzled about it. Finally, on very helpful individual recommended recycling the application pool. I figured it couldn’t hurt so I gave it a shot and tried to reconnect. It worked!! So, if you are getting this same error, recycle your application pool for the site you are connecting to and try again. It should work.