We verified the file exists on the ftp site and stages ok on a development deployment. Please verify the proxy settings. Please verify when you installed the appliance you used thick provisioning and did not change the amount of RAM the VM uses.  If those are all good you will likely need to call into support and give them your log to see what’s going.  When calling in provide the service tag of a server that has pro support and tell the call directory you need help with VMware and the vCenter plug-in VMware in the advanced virtualization queue. The experts are there. 
Steps: 1. Click Firmware 2. Run Firmware Update Wizard 3. Update from repository: The repository will download the update catalog from Dell Online (ftp.dell.com) 4. Select System Bundle (Windows)PER710 v484 5. Select BIOS and IDRAC update (Server BIS 11G, 6.4.0 and iDRAC6, 1.96. A00) 6. Select Enter maintenance mode, apply update(s), the reboot.      Option on, Exit maintance mode after firmware udpate completes Recent Tasks reports the Staging of 2 file(s) for update Dell Hardware Update Task nl01esxi001.OURDOMAIN Completed Staging 2 file(s) for update. OURDOMAIN\_svc_DellVCplugin VMVC001.OURDOMAIN 07-Jan-14 12:26:56 PM 07-Jan-14 12:26:56 PM Dell Hardware Update Task nl01esxi001.OURDOMAIN Completed Staging file (ftp.dell.com/FOLDER01631931M/1/R710_BIOS_4HKX2_WN32_6.4.0.EXE). OURDOMAIN\_svc_DellVCplugin VMVC001.OURDOMAIN 07-Jan-14 12:26:56 PM 07-Jan-14 12:26:57 PM After some minutes: Dell Hardware Update Task nl01esxi001.OURDOMAIN Cannot complete the operation. See the event log for details. Failed staging file (ftp.dell.com/FOLDER01631931M/1/R710_BIOS_4HKX2_WN32_6.4.0.EXE) on the remote share (172.17.2.66:/nfsstage/repository). Details: None. OURDOMAIN\_svc_DellVCplugin VMVC001.OURDOMAIN 07-Jan-14 12:33:38 PM 07-Jan-14 12:33:38 PM
Firmware update: Failed staging file