The system firmware has changed the processor's memory type range registers (MTRRs) across a sleep state transition (S4). This can result in reduced resume performance.

I don't recall getting this Event 137 message before upgrading from Win 7 to Win 10.  Maybe I just missed it.  Also, I do get the error in both a desktop machine that is set not to allow hibernation, and a laptop that uses both hibernation and sleep frequently.  Neither has UEFI BIOS.  Nevertheless, despite OrionsToy's excellent comments and those of many others, I find that on the laptop, as well as on the desktop, I get only "The system firmware has changed the processor's memory type range registers (MTRRs) across a sleep state transition (S4)."  I never get a mention of the (S5) state. It may be that in my case the message only occurs with sleep, but not with hibernation.

The real problem with this error message (and many others in the Windows Event Viewer) is not just trying to understand whether it is in itself truly significant or not, but that it is impossible for a user to determine, without extensive research (like finding then reading this entire thread) whether it is important to the problem that you have.  In my case, I was forced to look at it (like a couple of other posters here) because of a real return from sleep problem which gives me a blue screen, but creates no other useful events in the event viewer.  So I was forced to default to probably wasting my time researching this error message, which most likely has nothing to do with my problem,...or does it?

This happens a lot with Windows 10 on two different computers.  It never happens with Windows 7 on the same computers.  I have hibernate disabled on all my computer installations.  "powercfg -h off"

Windows 10 needs a lot of cleanup.  In the meantime, "Viva la Win7".

Yes, I found it helpful but not satisfied. You would think that in this day and age as advanced these computers are this would not be an issue. We should be able to remedy these issues with out having to go through all this, Very complicated. it seams the faster and so called convenient systems are supposed to be the more time consuming  and at times labor intensive it all is. I just don't know,I want to thank everyone for  there time and advice it was insightful and I learned  some things along the way Thank  you.

Since this error occurs with hibernate disabled, disabling hybrid sleep will  do nothing. When hibernate is disabled you don't even have an option to disable allow hybrid sleep.

As I stated in other posts on this thread, It doesn't matter what you do the error will come back ... it will change if you use hibernate or sleep(s3) ... if you use sleep it will be an error with hibernate(S4) error, if you hibernate it will be an error with shutdown(S5).

So it doesn't matter, the error will just show for the "next" power state. If there was a S6 then the error would probably show up every time you shutdown(s5)

You may want to disable "Allow hybrid sleep" in Power Options