Cisco UCS C210 M2 ESXi 5.1 Stuck At 'Initializing scheduler....'

After upgrading a Cisco UCS C210 M2 rack mount server to ESXi 5.1 and then ESXi patches from 25/07/2013 the host was stuck at ‘Initializing scheduler….’ I had checked my firmware version was satisfactory for ESXi 5.1 but found reports suggesting this (intermittent) issue has been around for a while with earlier versions of ESXi, different versions of UCS models and firmware and maybe HP models too. Before trying the suggested workaround of disabling legacy USB support, I decided to get the box up to the latest firmware.