I may have a work around for this.
Tested on Windows 10 2004 to Centos 6 systems. Samba 3.6.1 with SMB1 disabled and using SMB2
As suggested when running net use under system with psexec no joy in creating the share. Ran a wire shark trace noticed that the username was not been populated on the NTLM Auth response
Entered the full user name as HOSTNAME\User and it worked. Tried the same in Duplicati and it then came back with a successful test connection.