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After the latest upgrade the PRTG probe service does not start



The service just sits on stopping and you cannot force it to stop with access denied. A reboot does not allow the probe to start.

Running on Windows Server 2016

probe prtg service

Created on Nov 27, 2019 11:08:37 AM

Last change on Apr 22, 2020 6:10:38 AM by  Maike Guba [Paessler Support] (2,404) 2 1

4 Replies

Accepted Answer



There is "quick fix" explained for the issue further down, but before proceeding with that, it would be great if someone could perform a few tests -especially when the issue occurs with the PRTG server's own local probe- and provide us the result, so we can find the root reason for the issue that occurs in some installations:

Please download this connection tester for a few quick tests.


  1. Unzip into a folder of the affected machine (keep the cert subfolder and all files)
  2. Start PRTGConnectionTesterServer.exe
  3. Click "Start"
  4. Start "PRTGConnectionTesterClient.exe"
  5. Click "Start"
  6. Server should now show something like this: 19.11.2019 10:36:04 Start 19.11.2019 10:36:04 GID: {9E52E810-512B-467C-A483-3B61CF26CA42} 19.11.2019 10:36:04 (20312) SetActive 1 19.11.2019 10:36:11 (9936) Connect from []:58324 19.11.2019 10:36:11 BeforeSSL: 19.11.2019 10:36:11 (9936) Version=5678 19.11.2019 10:36:11 CheckPassword IP: GID:{C38E81A9-0A56-4423-9E55-3B35DF456EC7} Hash:1234 Version:5678 19.11.2019 10:36:11 (9936) Pass ok 19.11.2019 10:36:11 (9936) Send GID: {9E52E810-512B-467C-A483-3B61CF26CA42} 19.11.2019 10:36:11 (9936) Login OK 19.11.2019 10:36:11 Connect {C38E81A9-0A56-4423-9E55-3B35DF456EC7}

So far, so good, next steps:

  1. Click "Hello World" on the client
  2. Client and server now should show some new sent and received messages
  3. Stop server and client
  4. Repeat above but disable the "Use SSL" checkbox before clicking "Start"
  5. Now copy the log content of Client and Server (right click to select all and copy) and send it to us by email ([email protected])

The aforementioned "Quick Fix":
The issue is related to software component "NPCAP" that comes along with PRTG and also received an update, it can be uninstalled manually from "Installed Programs", but it won't uninstall properly as long as "PRTG Probe" is still running. If you can't kill "PRTG Probe" manually:

  1. Open services.msc
  2. Double-click "PRTG Probe" and set Startup-Type to "Disabled", then reboot.
  3. After that you should be able to uninstall NPCAP
  4. Make to sure to set Startup-Type for "PRTG Probe" again to "Automatic".
  5. I would recommend to do another reboot, then probe service should work again.

Kind regards,



Created on Nov 27, 2019 12:18:14 PM by  Erhard Mikulik [Paessler Support]

Last change on May 26, 2020 8:40:20 AM by  Maike Guba [Paessler Support] (2,404) 2 1



Super star! Thank you Erhard! That worked.

Created on Nov 27, 2019 12:32:27 PM



This also happened to me, running Win 2016. Steps above worked correctly although NPCAP is not reinstalled?

Created on Nov 27, 2019 1:16:00 PM



The whole purpose of NPCAP is that it is used by packet sniffer sensors, nothing else, so when NPCAP is missing, PRTG will still work, but you can't use Packet Sniffer sensors on the probe where it was uninstalled.

Created on Nov 27, 2019 3:52:34 PM by  Erhard Mikulik [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.