Same problem.

I'm in China, and when I made a call to the dell support, the engineer No.1054037 want me to reset my computer, and instead on his judge that was I installed the wrong version of BIOS. 

My BIOS ver is 1.6.1 and the dell engineer told me the right one should be 1.5.1. 

Any Dell engineer can explain it to me? 

Adding myself to the list of affected users (Dell XPS 13 9350)

I too will add myself to the affected victims

Me too

Yep, me too!

Come on Dell, pull your finger out

Have the same problem on my 9360.  Geez, great job Dell!  There's no possible way they tested this dang BIOS "update".

It's also obvious that no one at Dell even follows these threads since I haven't seen one post by Dell saying something simple like "we're sorry and we're working on a fix".

If you have Support Assist downloaded on your computer delete the program and it should fix the problem. You will still get notices for upgrades. However, it will not be through Support Assist. Dell is having problems with Support Assist and their fix is to delete Support Assist.

Delete Support Assist Program. 

Sorry but I get the same error when I try to flash the BIOS through the built-in BIOS Update option accessed by hitting F12 at boot.  ...Not going through Windows.

I have read through this thread because my issue is exactly the same as the OP.  Delll XPS 13 (9350) with BIOS 1.6.1 that keeps wanting to install new BIOS with the same error message about unsupported downgrade.

My only question is did I already make a mistake by installing 1.6.1 or is that BIOS version safe/okay?   I'm fine ignoring the messages to update but I'm just wondering if I'm already in trouble?  Everything works fine at this point.

Thank you.

same problem here, BIOS downgrade is enabled in BIOS settings, but when I run the BIOS version I wan to install (as an admin) it still prevent me from downgrading.  uninstalled all DELL support stuff as recommended  in this post, but still nothing...

My question - at this point - is not really how to downgrade my BIOS, but if I even need to since I'm one of the lucky ones where my machine still boots and works.  My fear is that if I start trying to "fix" it back to 1.5.1 that I will end up with something that doesn't work because something went wrong in that process.

As a registered Dell product owner, I would have expected an email or something from them about this.  Since that hasn't happened, my question here is:  If everything works, can I leave it as is and wait for Dell/Intel to come up with a fix or path forward from 1.6.1 or do I need to remove 1.6.1 from my system?

Thank you.

I understand the problem is that you had 1.6.1 which Dell pulled because Intel told it was unstable, so assist wants to downgrade to 1.5.1. Which probably gets prevented by BIOS. Try booting into BIOS, go through the menu, find the setting which allows/prevents BIOS downgrade, set it to allow, save and reboot. I saw such a setting in the 9550 BIOS menu. 

X{S 9365  just arrived have not updated.  Does anyone know if a BIOS problem has been reported for the 2 in one model.