A few things to check when configured to use HOTADD transport mode..
1. HotAdd transport is supported only on a virtual machine backup proxy
2. no anti-virus should be running on backup proxy host during the backup
3. automount should also be disabled on windows backup proxy host
(refer " )" target="_blank" rel="nofollow noopener noreferrer">http://pubs.vmware.com/vsphere-60/index.jsp?topic=/com.vmware.vddk.pg.doc/vddkBkupVadp.9.6.html&resultof="vss" )