While I was trying to update an iLO from version 2.00 to 2.27 on a HP DL360 G6, I was seeing the firmware update fail in Windows, the error back was that the hardware installed in the server was incorrect. Installing the firmware through the iLO web page itself just failed, appearing to timeout when attempting to upload the image.
The fix for this, oddly enough was to use Firefox. When doing the same update to the iLO in Firefox, the image does get uploaded and the firmware update then completed without any problems.