Backup fail with exit code 71

Problem:
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The files in the file list did not match any of the files on the client. This error can occur with only one file in the file list and the file
cannot be backed up due to an I/O error.

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We are trying to backup a slice from SAN mounted on c\ drive as folder and receiving the above error. have any one experienced this issue.

netbackup 7.7.3 just upgrade

NBU master is windows and client is a hyperv server. the media server is configured on the same client for FC backup to storeonce vtl device.

Every other folder on the C:\ drive of this client is accessible and is being backed up successfully. on this sliced folder is problemetic.

Interestingly, the backup of this folder is successfuly when tried over LAN on a SAS directly connected library.

please help, if someone has encountered this issue.