SIRIS, ALTO, and NAS: Error: Backup failed due to unknown error in the agent software (BK006)



When you try to start a backup for a system protected by the ShadowSnap agent, you receive the error message, "Backup failed due to unknown error in the agent software."

In legacy versions of the Datto IRIS environment, this error message was "Errno 4 Interrupted Function Call."


  • ShadowSnap Agent


  • "Backup failed due to unknown error in the agent software" is a ShadowSnap error which signifies an old or corrupted installation of ShadowSnap.


  1. Make sure the ShadowSnap agent meets all setup and compatibility requirements.
  2. Repair agent communications by following the steps in the SIRIS, ALTO, and NAS: Repairing Agent Communications article.
  3. Attempt another backup.
  4. If the issue persists, from the device UI, force a differential merge.
  5. Attempt another backup.
  6. If the issue continues to occur, reinstall the ShadowSnap software by following the steps in this article.
  7. Attempt another backup, and observe the results. If you are still unable to capture a backup successfully, contact Datto Technical Support for further assistance.

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