I have been having this problem for over 6 months, and, to be honest I have got past this issue by doing the work at home, however this is not practicle as there are engineers I work with who still cannot get this issue resolved.
Problem:- Windows 7 or Windows 8 vanilla build with all the required MS Updates, downloaded the latest version of the RIM Desktop Manager Software downloaded from web site. The PC as never performed any upgrade on a BB phone at all. We wipe the device on another PC with BB Tools, so it reloads with the familar white screen 503/50x no OS, we then plug the phone via USB into the newlyrebuilt PC with latest BB Desktop Manager software. It goes through the standard reboot and prompts that the phone requires the OS to be loaded, we, let it do this, but it then prompts that it needs to perform a update, it then presents you with the Update Blackberry Software, and fails, thus not allowing us to perform an OS update or reload.
I am at a loss we have checked with our networks team, thinking that perhaps it was due to a firewall restriction as I managed to perform a repair at home not on the corporate network. However, there was nothing in place to prevent this, in addition to this an engineer who lives 150 miles away also tried to perform this from home, on the same ISP and it failed as per the issue we have when on the corporate WAN.
At a complete loss any one help. Remeber we are doing this on vanilla built PC's that have never performed a update before, so there is no need to delete the vendor.xml file etc.
We mainly take 9720 phones, but we have found that this does not work with other models either.