Jtdylktuy

I'm using the Windows 10 preview on a couple of machines (a laptop, and a server-2012-hosted VM). On the VM, Windows shuts itself down about every hour and has to be restarted from the Hyper-V console.

There's no indication of any error; the screen shows "shutting down", and the event log records an event from the User32 source saying that NT AUTHORITYSYSTEM is shutting it down:

The process wlms.exe has initiated the power off of computer XXXXXX on behalf of user NT AUTHORITYSYSTEM for the following reason: Other (Unplanned)

 Reason Code: 0x0

 Shutdown Type: power off

 Comment: 

I can't say for sure, but although it's reminiscent of a "sleep" due to inactivity, my impression is it's not related to activity. I think it's happened at times when it was used a few minutes ago.

This issue doesn't happen on the laptop, which just stays on.

• 
  EDIT adding info about the build versions in use. Both machines cited are on build 10074. If anyone reading this is perplexed that
  someone would use anything other than the latest build (currently
  10130), remember that during a technical preview not everyone is
  expected to be, or wants to be, on the latest build. Users can select
  whether to be on the slow ring or the fast ring,
  which determines how quickly they will receive updates for new
  builds, which in turn means in theory they can defer updating until a
  new build has had a chance to prove its stability. Additionally it's
  in the nature of a pre-release product that whole areas may not yet
  work properly (even 30 days pre-RTM!) and issues are still being
  resolved. If you look on the Windows Feedback app you'll see numerous
  posts relating to failure to update to the current build (10130).
  This failure is afflicting the two machines I've posted here about, and I'll be continuing to work with whatever MS push out in response to the broken 10130 update feedback, in the hope that any findings from this exercise can ultimately contribute to the stability of the RTM version. I
  use a different VM with a clean install of 10130 for using 10130.


• Returning to my question, it's by no means clear that this should be
  an issue only with build 10074 (and indeed the other machine on 10074
  is not afflicted by this issue). Nor have I seen a single post
  linking this issue to build 10074. In the absence of any information
  to the contrary, we must assume it's an issue that could affect any Windows 10 build or any version of Windows. END EDIT
  

I've searched and found reports of similar messages in various scenarios and Windows versions, but not a simple unexplained shutdown like this.

Why is it doing this, and how can I stop it?

This happens when Windows 10 has failed to activate.

Windows 10 activates automatically whenever it has an internet connection; if it fails to do so, it may succeed after a restart. It seems such restarts are now automatic, without any notification that activation has failed.

If the failure is for reasons that a restart won't help with, such as the DNS name does not exist issue, Windows 10 will keep restarting periodically to try and activate, in an endless loop, never succeeding in activating.

Within Settings there's a section for activation. Press the Activate button. If activation fails here, you are shown the reason for the failure, such as "DNS name does not exist". Armed with the failure details, you can now do a search for the particular issue encountered, and take the necessary steps to resolve the activation issue.

Further information about activation in Windows 10 and resolving activation issues can be found here.

Same issue, I've disabled windows software protection service and that's it.

HKLM/SYSTEM/CurrentControlSet/Services/sppsvc

You need to set value 4 for Start dword and reboot.

Look like the Windows 10 Preview license have been expired. Is it running the same preview version as the laptop ?

Please run Windows Update to latest build to see whether it fixed this issue.