Remote client issue with Catalina in Retrospect 9 or higher for Macintosh Posted 12 hours ago · Edited 5 hours ago by DavidHertzberg P.S.: Have you simultaneously made changes to either your "remote Mac" hardware or how you operate it? · Report reply bookcent/Steve, First of all, "backup client not found" is error -530, not -503. I presume you have taken steps 1-5 in this ancient Knowledge Base article. Second, I solved a 2-year-long problem with -530 errors by Removing my MacBook Pro client from Sources and re-adding it using Add Source Directly—after having assigned the MBP a fixed IP on my router using its MAC address (stands for Media Access Control and has nothing to do with Macintosh, obtained from System Preferences -> Network -> Advanced for active Ethernet connection -> Hardware tab), per pages 66 and 79-80 in the Retrospect Mac 16 User's Guide. You speak of "remote Macs"; are these "clients" possibly on a different subnet from your "backup server"? If so, Subnet Broadcast, per page 79 in the UG, may work for you instead of Add Source Directly; it worked for me when I briefly tried it in late 2018 per henry-in-florida's suggestion. Third, once you have eliminated the -530 error, upgrading your remote Mac to Catalina means you'll have to comply with this KB article to fully access it with Retrospect. This KB article is also applicable, but you have complied with its current contents by upgrading your "backup server" to Retrospect Mac 16.5.1.(104); Retrospect "inc." promised new contents several weeks ago, but so far there's been no update of the article. P.S.: As Nigel Smith has pointed out below, while I was writing this you started another thread. In that one you mentioned a "multicast port unavailable" message; have you simultaneously made changes to either your "remote Mac" hardware or how you operate it (i.e. use of wireless)?