Downgrade Firmware

[04291986]

I'm trying to downgrade my SM-G928I from Android 6.0.1 to Android 5.1.1

I've been getting this error on Odin:

"<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/008> Odin engine v(ID:3.1101)..
<ID:0/008> File analysis..
<ID:0/008> SetupConnection..
<ID:0/008> Initialzation..
<ID:0/008> Get PIT for mapping..
<ID:0/008> Firmware update start..
<ID:0/008> SingleDownload.
<ID:0/008> sboot.bin
<ID:0/008> NAND Write Start!!
<ID:0/008> cm.bin
<ID:0/008> FAIL!
<ID:0/008>
<ID:0/008> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)"

and on my phone's display:

"SW REV. CHECK FAIL. DEVICE: 3, BINARY: 2"

Could anyone tell me what it means? and how can I solve this problem?
Please reply ASAP! Thank you