HotAdd transport mode is failing

Backup server is a VM, SCSI disks, VM datastore is accessible from the backup appliance(VM), using vCenter logon credentials.

VMware log:

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2014-08-01T14:58:35.133-04:00 Checking transport mode hotadd.

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2014-08-01T14:58:35.133-04:00 Transport mode hotadd passed pre-flight checks. Adding to list of available transports.

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2014-08-01T14:58:35.133-04:00 Confirmed that mode hotadd is applicable.

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2014-08-01T14:58:35.274-04:00 The host host-35 is licensed for HotAdd

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2014-08-01T07:26:48.244-07:00 Established NFC session for metadata and disk signature access.

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2014-08-01T14:59:24.462-04:00 Mounting VM vim.VirtualMachine:vm-83 using transport hotadd failed : Could not open disk for disk signature retrieval..

2014-08-01T14:59:24.462-04:00 Cannot use mode hotadd to access xxxxx/xxxxx-000002.vmdk: Cannot mount using this method.