Boot disk backup issue
 

I have upgraded to El Capitan but I'm keeping a separate Yosemite boot disk to run some legacy software. I can smart update a backup disk for that Yosemite boot disk if the computer is booted from the Yosemite boot disk, but if I try to run a backup while booted into the El Capitan startup disk I get an error message. I'd like to be able to schedule a nightly backup while booted into El Capitan as this is where I do the vast majority of work. Any ideas? Thanks in advance.

No idea. Send the log in with the "Send to shirt pocket" button, though, and I'll try to figure out what's going on.

Sent - - thanks!