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Resolving HTTP 417 Error In ARC

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I am experiencing an issue this morning with the following error message in Synthiam ARC:

Version: 2025.06.22.00

System.Net.WebException: The request failed with HTTP status 417: Expectation Failed.
   at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
   at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
   at ARC.com.ezrobot.www.apps.WebService.GetPlugins(String[] GUIDsToIgnore)
   at RKUcwiabYs6XhKUTStt.KPjB6PauHWtitgrdWKh.Hega6YVqvW()

It seems to be related to a web service call while trying to fetch plugins. Could someone help me understand why I'm encountering an HTTP 417: Expectation Failed error, and how I can resolve this issue in ARC?

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#2  

Hi - Athena here. That Synthiam_Support note is exactly right: a corporate/education firewall or proxy that blocks or inspects outbound HTTPS can cause HTTP 417 (Expectation Failed) when ARC tries to call the cloud webservice to fetch plugins. Below is a concise troubleshooting checklist, instructions you can give to IT, and next steps you can run and share with me so I can help further.

What to tell your IT team (copy/paste)

  • ARC requires outbound HTTPS (TCP 443) to these hosts:
  • Please allow outbound HTTPS (TCP 443) to those hosts without intercepting or modifying requests (no SSL/TLS re-write/inspection). If SSL inspection is required, ensure it does not rewrite expected headers or block clients using Expect:100-continue.
  • If your environment uses an outbound proxy, ensure ARC respects proxy settings or that the proxy allows these hosts.

Relevant Synthiam doc:

Quick troubleshooting checklist (follow in order)

  1. Update ARC

  2. Force plugin refresh

  3. Isolate the network

    • Try connecting your PC to a different network (mobile hotspot/home network). If it works there, the original network is the root cause (proxy/firewall/VPN).

  4. Check Windows proxy/VPN

    • Control Panel Internet Options Connections LAN settings. If there’s a proxy, try disabling it temporarily for testing.
    • Disable any VPN and retry.

  5. Disable HTTPS inspection / antivirus scanning temporarily

    • Some AV / corporate security appliances perform HTTPS inspection and can break SOAP calls. Temporarily disable HTTPS scanning (or antivirus) for a quick test, then re-enable it.

  6. Capture logs with the Debug skill

  7. Send a Diagnostic Report (if you want Synthiam to inspect environment details)

Optional technical test

  • Try opening https://synthiam.com or the admin endpoint from the same PC in a browser. If the browser shows proxy/certificate errors, that confirms network interception.

What to send me so I can help next

  • Are you on a corporate/education network or behind a proxy/VPN?
  • Does ARC work on a mobile hotspot?
  • Did deleting AvailablePluginsList.txt + restart change anything?
  • Paste the Debug skill log entries around the time of the 417 error (use the Debug skill kebab menu to copy and paste here).
  • If you used Diagnostic Report and sent it, tell me that it was sent and approximately when.

If you want, I can draft a short email you can paste to your IT department with the whitelist request. Would you like that?


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