Time capsule backups fail because disks aren't recognised - how to fix?

Question

Hi, all... I have a 500GB TC with a 2TB Western Digital drive attached, which I use for backing up three computers. My desktop iMac is connected to the TC by Ethernet cable, my laptop and my wife's laptop connect over wifi. The desktop and my wife's laptop back up to the WD drive. My laptop backs up to the TC internal drive.
Every few days (max, min is something like 1 day), I notice that the backups are all failing at the "Looking for backup disk" stage. That's both the iMac connected by Ethernet and the laptops on WiFi. The WiFi _signal_ is fine -- my laptops can see the network, browse to other destinations, download files at a good speed. The TC has a green light, and Airport Utility doesn't detect any issues.
But although the TC appears in the Finder Sidebar, it shows no disks. If I try to "Connect As" nothing happens.
I can resolve the issue by pulling the plug on the TC and re-powering it, and then doing the same with the WD disk. If I do that, both disks appear in the finder (with no need to "connect" to them) and backups proceed normally.
Backups can go on normally for anywhere between 8 hours and four days, but then I have to repeat the whole rigmarole to get them started again.
I'm beginning to suspect something to do with two backup processes over Ethernet and Wifi to two different backup disks "colliding" somehow and locking out the disks. I say this, because if I'm away for a week with my laptop, and my laptop does no backups to the TC in that week, then when I get back, the iMac is still backing up fine, even though five days is a long time compared to how often it seems to fail when all three machines are at home and backing up.
I don't want to have to keep pulling the plug, so does anyone have any ideas?
Many thanks!
bestest,
M.

Answer 1

Still not resolved this. However, I'm now absolutely SURE that it's something to do with colliding back-ups locking the TC up somehow.
I was at home for 3 weeks over Christmas, without using my work laptop. All through that time, the iMac continued backing up to the WD with no problems. Since then, though, I've been using my work laptop at home all day for a couple of weeks, and pretty much every afternoon, mid afternoon, the iMac alerts me that the backups could not be completed because the backup could not be found.
The TC shows up in the Finder sidebar still, and if I run Airport Utility I can access it and administer it. Once again, if you click on the TC in the Sidebar, it just says "Connecting" and shows no disks. However (and this is a new discovery), if I use the Airport Utility to "Disconnect All Users" from both the TCs internal disk and the WD external disk, the TC disk reappears in the Finder. The WD disk can only be made to reappear by power cycling it. But once that's done, backup can begin again as normal.
I therefore don't have to power cycle the TC to get the disks back.
So, it seems that something is happening that means that when two "users" are connected to the disks, having attepted a backup, they are locked, and can't be connected to.
Throughout all this, though, the laptop has continued to back-up normally to the TC internal drive, so IT can still see and connect to that drive. It's just the iMac that is somehow locked out of the TC and its external WD backup drive.
I do wish somebody would fix this!!!!
bestest,
M.