Oh well, #sigh
I have a few Macs.
All on WIFi
All on DHCP
They have to be this way, because they roam from office-to-office, client-to-client, home-to-work-to-home ... like laptops do.
The error -530 and associated -519 has be around in almost every version of retrospect I have used for the past 20 years.
I can never find the solution, apart from a full client reinstall, and I can not be doing that every week TBH!
Is there ever going to be a stable answer?
Each Mac, Client and Server has no firewall or anti-virus FYI.
The fixed desktop Laptops that do not leave the office have no issues.
The laptops returning to the office login automatically to the WIFI and have no network issues for everyday work; email, www, ftp, server shares, printing ... what so ever.
Server: Mac OSX 10.11.6
Client: OSX 10.12.6
Please don't say 'upgrade to the latest version of Retrospect or I may have to slap you :-)
That has never been an answer to this issue.