The error is reported during attempt to backup VADP set.

GetBackupSessionFiles failed. error: The server refused connection (VixDiskLib_Open returned error code: 14009). 

([Path to the VMdk) failed OpenListing for IP\vCenter\ServerName\


The actual problem was SSL protocol not supported (old versions tls.protocols=tls1.0,tls1.1,tls1.2 ). This happen because one of the ESXi hosts was version 5.1 (not supported),


Migrate the VMs to the esxi version 5.5 and above.