What does Windows error code 789 (ERROR_LOST_WRITEBEHIND_DATA_NETWORK_SERVER_ERROR) mean?

ERROR_LOST_WRITEBEHIND_DATA_NETWORK_SERVER_ERROR

delayed-write data was lost because the remote server returned an error.

ERROR_LOST_WRITEBEHIND_DATA_NETWORK_SERVER_ERROR indicates this condition: The client remained able to communicate, but the server rejected or failed a write that Windows had queued. Server-side storage exhaustion, quotas, failover, permissions, file-system errors, or an SMB implementation failure can all produce this distinction.

Where the result appears

• remote writes that fail after buffering on the Windows client.
• clustered file-server failover or storage outage.
• NAS devices returning an error during cache flush.
• applications closing a remote file after a server-side allocation failure.

What to collect

• the server-reported SMB status and any translated Win32 code.
• server disk capacity, quota, file-system, and cluster events.
• the remote path, share configuration, and durable-handle state.
• file length and checksum on both client expectation and server reality.

Handling and recovery

Investigate the server before retrying. Free capacity or fix the server-side fault, then recreate or verify the entire affected file. For transactional outputs, write to a temporary name, flush, validate, and rename only after the server confirms durability.

Common misinterpretation

This variant is not primarily a cable or Wi-Fi problem. The network delivered the request far enough for the server to return an error.

References

• Microsoft: System error codes 500–999