SharePoint Designer error: Value does not fall within the expected range

After checking out a page to edit using SharePoint Designer I was presented with an unfamiliar error:

soap: ServerServer was unable to process request. —> Value does not fall within the expected range.

This is the first time I have encountered this error but after a bit of investigating I discovered this was caused by opening the site using the wrong URL – I used the server name (http://ww-sp-01) instead of http://intranet).  When opening the site using http://intranet the error is not generated.