I just wiped the BB with JL_Cmder and have the 507 error message on the screen as expected. Following these instructions I start Desktop Manager and expect to see a prompt for upgrading... except there's nothing.
When I start the Application Loader I get a message saying "The BB Desktop Software does not have BB Device Software for the Device that you have connected to the computer".
Ok thanks, it's updating now. I re-read the instructions very carefully, and realised I had deleted the Device.xml and not the Vendor.xml file. Classic