Time Machine error 19

I'm having the same issue. Backups ran fine until a few weeks ago. Now I get error 19 over and over when I try to run a backup to my WD MyCloud NAS over Time Machine.

Computer: M1 Mac mini running MacOS 13.1, connected via Ethernet to my router

Drive: WD MyCloud running the most recent firmware, 5.25.132. Its Time Machine Backups feature is enabled. It's also connected directly to the same router as the M1 mini, via Ethernet.

The M1 mini keeps telling me this:

"The backup disk image “[My computer's name].sparsebundle” could not be accessed (error 19)."

Troubleshooting thus far:

• I can connect to the WD MyCloud disk just fine, both through the Finder and via WD's web-based interface. The drive is in good health according to its own diagnostics.
• I had this same error on the M1 mini when it was only running MacOS 13.0. But it had previously backed up just fine with Ventura.
• Other Macs in my home, including an M1 MacBook Air running at least MacOS 13, and a much older MacBook Pro running Catalina, can back up fine to the WD MyCloud drive over the network. The M1 MacBook Air is backing up as I type this. Which kinda scotches my theory that the problem lay with a firmware update from WD.
• As WD instructs, when I point Time Machine at the TimeMachineBackups share on the WD MyCloud drive, I connect to the drive as a Guest, rather than with my admin account and password. (Though I'd previously been able to back up while connected as admin.)
• Time Machine appears to hang on the "connecting to backup disk" stage of the process. It chews away at that for a minute or two, and then the dreaded error 19 appears.
• I get that error message even when there is no sparsebundle file whatsoever for the computer in question. It's like my computer is creating a sparsebundle file for itself, then telling me it's unable to find the file it just created.
• I've tried deleting the old backup sparsebundle file, both by telling Time Machine to do so, and manually from the TimeMachineBackups share on the WD MyCloud drive via the Finder.
• Yes, I've tried turning it -- both the M1 mini and the WD MyCloud drive -- off and on again.
• I've tried turning off Time Machine Backups on the WD, rebooting the drive, and reactivating Time Machine Backups.
• I've tried wiping the WD MyCloud drive back to factory settings, which obliterated all my other computers' backups, but did not enable this one.
• My computers all have unique names, so it's not like one of them could be getting confused and trying to back up to another's sparsebundle file.
• I've considered traveling back in time to when Apple's software lived up to its "It Just Works" branding. Alas, I lack the necessary technology.
• Help, please. Thank you.

I seem to have fixed the problem, but I'm not sure how. Here's what I did before it started working; any one of these steps alone may have fixed the problem, or maybe they all did.

• I switched off "Time Machine Backups" on the WD MyCloud under Settings > General.
• In the MyCloud web interface, under "Shares," I deleted the "TimeMachineBackups" share and all the data inside it, leaving only the "Public" share remaining.
• I switched "Time Machine Backups" on again under Settings > General. I used Public as the share for backups.
• I noticed that on my Mac's hard drive, under [The Name of My Hard Drive]/Volumes, there were 99 files of zero KB apiece marked "Backups of [My Computer's Name]." I deleted all of those.
• And when I set up Time Machine, pointed at the Public share of my WD MyCloud and connected as Guest, it backed up!

Hope this helps anyone having similar troubles. Joanna, I'm glad your problem got resolved, too.

WD makes a number of different kinds of hard drives. Could you check and provide the model number of the product you have so we can learn more about it by doing a web search?

Does the WD drive connect directly to your MacBook Air, or is it connected to another device?