I'm trying to create a page layout on SharePoint 2010, based on a new Page Layout Content Type subclassed from the Publishing Content Type "Page". I got the new content type created ok, with existing site columns added fine using SharePoint Designer, and some new ones added with the web interface. When I try to create the page layout with SPD, I get a bizarre blank alert popup asking me to "OK". I "OK"ed I notice the page layout has been created.
Then I follow instructions in  to open the toolbox "Page Fields" & "Content Fields" but I see this error in SPD under each of "Page Fields" & "Content Fields":
ERROR:"Controls in this category require a Microsoft SharePoint Publishing Page Layout" in the Toolbox pane.
The publishing site collection feature is activated in "/support", as is the publishing site feature in the site I want the page layout: "/support/learning".
 Book: Microsoft SharePoint Designer 2010 Unleashed (2011) Kathy Hughes (SAMS), chapter 15
I repeated these steps on our pre-production farm and did NOT get the error. I still have it on production...