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Here is the uncommon SENS problem on my Win 7 computer:

  • The message of "Failed to connect to a windows service (could not connect to System Event Notification Service)" first appeared after installing Windows Update KB4539601 and the necessary computer restart. Slow log-in/out, the taskbar went to the grey classic theme instead of the Aero theme, audio service took time to load...

  • I tried to solve the problem by resetting "SENS" & "COM+Event System" in services.msc, and resetting Winsock Catalog with cmd. They worked at the first time of restarting the computer but the problem happened again after starting the computer the other time.

  • I went through some posts in various communities and tried to uninstall the mentioned Windows Update as suggested in this post: https://answers.microsoft.com/en-us/windows/forum/all/system-event-notification-service/03db6f99-e246-4925-88c8-2a6620c33eea?page=2

  • The uninstallation and computer restart took hours to complete. The Windows appeared to be normal for a time but the SENS problem re-appears every time I restart the computer. The suggested uninstallation did not work for my case. Also, resetting services & Winsock Catalog no longer work...

*** Perhaps a useful finding: the SENS problem would be solved one-off if I manually log out the user account and log in again (coming with a minor problem on delayed shut-down of explorer.exe "playing log-off sound effect" when logging out/shutting down). However, the SENS problem happens again whenever I boot up / restart the computer.

Any idea on the solution?

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  • If removing the update has not resolved the problem that indicates the cause of the problem more than likely isn’t actually the update. What other changes to the system happed at the same time? The fact it took hours to uninstall and reboot indicates a hardware problem (storage device). – Ramhound Mar 4 '20 at 12:50
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I am facing the same problem as you on my 3 machines under Windows 7. If you use Kaspersky Antivirus 2020, it is very likely that it comes from the patch (i) which was installed in early March. I contacted KAspersky technical support who identified a bug. He confirms to me that the latter will be corrected with patch (j) which should be released around April 14. This bug is due to a hash control error on a .asp file in the Kaspersky application. This system file integrity check at startup disrupts system services that start badly or crash. This explains the slowness, the famous error message and the AeroPeek HS themes. If you manually relaunch the SENS, Audio and Themes services, the problem is corrected until the reboot (new control of this file ...) In the meantime, there is a workaround that is to change the extension of this DLL. Apparently, this does not affect the normal operation of the application. But I cannot guarantee it completely.

https://community.kaspersky.com/b2c-forum-des-utilateurs-francais-66/inc-000011341527-mess-hachage-et-barre-taches-win-basique-7491

To rename this file, you must first go to the Kaspersky settings and temporarily deactivate the program's self-defense. Then you can rename this file:

C:\Program Files (x86)\Common Files\Kaspersky Lab\klhk\klhk_x64\ klhkum.dll

to klhkum.old

You relaunch Kaspersky's self-defense and you reboot to PC. Everything works normally again.

If you don't use Kaspersky then your problem is somewhere else.

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