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.
—————————-
13/10/2010 Update: You can use http://localhost/ and not get this problem by adding http://localhost/ as an entry to the Alternate Access Mappings in Central Admin.
Thanks buddy!!