The fix: Do a clean install on the Blade using the original HP Custom ESXi 5 image.
Details: After the firmware and Virtual Connect were upgraded - Using VUM to do the upgrade process worked only a few times. It didnt matter if i used the HP Custom ESXi 5 Image or an image I had created with newer drivers. The only guaranteed way to get it to install everytime was to install ESXi from scratch and wipe whatever was on the disk (in my case 4.1 U3). Note this only applies to the G6 Blades - all the G7s upgraded first time without problem using VUM and the HP Custom ESXi 5 Image.
Thanks for your help
Guy