Error: Critical backup failure during data transfer



When you try to start a backup for a machine protected by the Datto Windows Agent or the ShadowSnap Agent, you receive the error message, "Critical backup failure during data transfer."


  • Datto SIRIS
  • Datto ALTO
  • Datto Windows Agent
  • ShadowSnap Agent


  • This is a generic error message indicating backup failure. You can find the detailed error message in the Agent Logs on your Datto appliance.
  • This error message also displays if a machine protected by the Datto Windows Agent is out of disk space.


1. In the Datto appliance's GUI, click the Protect tab, and navigate to the affected agent on the Backup Agents page.
2. Search the Datto Knowledge Base for any errors banners shown for the agent to troubleshoot further. If you do not see an error banner, continue to step 3.
3. Click Show Backup Logs, as shown in Figure 1.2.
4. Click Show Agent Logs, as shown in Figure 1.3. A detailed error message relating to the backup failure will display in the logs. If you do not see any error messages, contact Datto Technical Support for further assistance.

Figure 1: Show agent logs (click to enlarge)

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