In SharePoint Designer 2010 I would always get the error message below when I try to open any list form (DispForm.aspx, EditForm.aspx, etc) for editing.
soap:ServerServer was unable to process request. —> Value does not fall within the expected range.
It turns out that this was because I used http://localhost/ to open the site.
Opening the site using http://hostname/ immediately solves the problem.