Failure happened on 'Source' side. Copy activity Error in Fabric

Question

Failure happened on 'Source' side. ErrorCode=UserErrorWriteFailedFileOperation,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=The file operation is failed, upload file failed at path: '/Tables/table_name'.,Source=mscorlib,''Type=Microsoft.Data.SqlClient.SqlException,Message=Error 0x5 occurred when opening a connection from distribution 1 to distribution 1. Additional details: '0xa(MWC service error: Server responded with error: 400)'. Please try to run the query again. If the error persists, please contact support.

Path exists and the copy activity was working until today. Tried multiple times same error.

Can anyone please help

Answer 1

Hi ,

Thanks for reaching out to Microsoft Q&A.

have you tried to find the root causes what would have caused this issue?

Permission or Token Expiry:

Token used by Fabric to write to the lakehouse or warehouse may have expired or been revoked.

Reauthentication might be needed for the linked service or workspace.

Path Lock / Corrupted Metadata:

Even if the path exists, sometimes stale metadata or concurrent write locks (especially if the file was open or the session got killed) can cause these issues.

Table/Path Corruption:

Fabric internal metadata or the target delta table might have become corrupted. This is not common but possible when aborted jobs leave stale temp files.

Backend Fabric Lakehouse Issue:

• "MWC service error" indicates an internal Microsoft Write Controller service problem - potentially a backend Fabric service issue (especially with error 0xa, HTTP 400).

Distribution Failure (Synapse-style sharding):

The part about “distribution 1 to distribution 1” hints at a possible issue in Fabric’s distributed write pipeline (esp. if Warehouse is involved).

Immediate Actions that you can try:

Restart the Runtime/Session

Restart the copy pipeline and Fabric runtime (especially the Spark engine, if used).

This clears temp states or hung sessions.

Clear and Repoint Destination Path

• Try changing the target path to a new directory ('/Tables/table_name_temp').

If that works, then the issue is likely with the original table metadata.

Revalidate the Linked Service/Connection

Re-authenticate or edit/save the linked service used in the Copy activity (especially if using Key Vault or OAuth).

This refreshes credentials and tokens.

Check for Concurrent Access

Ensure no other job is writing to or locking the same table/path.

• Look for active Spark sessions or long-running queries in Fabric Monitor.

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