Mark, another option is to update outside of the OS. You can reboot the server and hit F10 to access the System Service (Unified Server Configurator) and then select Platform Update.  You can select to get the updates from ftp.dell.com or you can provide the repository for it.  Let me know how it goes.
I have a PE 510 running Windows SBS 2011 and am trying to apply the firmware packs to my RAID1 and RAID5 disk arrays. FRMW_LX_R310809 and FRMW_LX_R311053. The Dell Update package detects the previously installed firmware and offers me an upgrade but only ever fails with 'The operation was not successful because the device buffer write has failed'. I have tried shutting down all the services as I read elsewhere on the Dell site that this was symptomatic of low resources but am having no luck. Has anyone any ideas? THanks Mark
Can't Upgrade Seagate Firmware