@Arash ,
It's likely that your flow is running on multiple nodes and each node is trying to process every file. When different nodes try to write the same file at the same time you get these errors.
You can change your flow to use a List-Fetch pattern. The ListHDFS processor should run only on the primary node and the output of it (the list of files) can be load-balanced across the nodes so that each node will FetchHDFS different files.
Cheers,
André
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