  Hello Did you follow the instructions in the release notes? [URL] If you are updating from anything lower than 15.5 then you have to step to 15.5 before you can update to anything later. Thanks
I have a similar issue. several Dell R720xd servers with a Gigabit 4P I350-t Adapter, and i can't get the firmware updated to 16.5.20 I am using the latest SUU dvd, from witin the lifecycle controller. The error message in the lifecycle controller is: SUP0520: Unable to update the Intel(R) Gigabit 4P I350-t Adapter firmware to version 16.5.20.  Any suggestions on how to get the firmware updated? The servers have ESXi6 as OS.  
Cannot update FW on Intel I350-t using LCC