time machine could not complete the backup
I have a 1st gen time capsule that I have been using for 5 years to backup a macbook with 10.6.8 on it. Recently I introduced a 2nd macbook with 10.9 on it and started backing up to the same time capsule. For a short time I was able to backup both machines to the TC without problem. Recently I introduced a new 802.11ac airport extreme to the mix and began using it as my primary wifi provider...the old 1st gen TC was connected to the extreme via gigEthernet and dropped from the wifi network. At this point I was able to continue backing up the 10.9 macbook but my old 10.6.8 client began showing "time machine could not complete the backup."
The rest of the dialog box reads:
"
The network backup disk could not be accessed because there was a problem with the network username or password.
Open Time Machine preferences to select the network backup disk and re-enter the correct username and password.
"
So I've used the airport utility to change passwords and try different combination of options for access but the error persists. The error persists whether connected via gigEthernet directly to the TC or via wifi through the new airport extreme. I can't get it to work. I've even tried removing the pair from the network and attempted a backup via gigEthernet with no other devices connected.
Interesting sidebar is that I can browse the network and connect to the TC without problem through the finder. I can see the .sparsebundle file for the old macbook. It is there just as it has always been but I can't continue backing up anymore.
-any thoughts on a remedy to this issue which doesn't involve me flushing the old .sparsebundle down the toilet? I really need to maintain the integrity of my old time machine backups.
AirPort Express 802.11N (2nd generation), OS X Mavericks (10.9)