I am still having this problem with my less than 1 year old 1 TB time capsule and my 27" iMac.
Odd times, for no good reason I get a message that my backup has been delayed because the backup disc cannot be found. A failure to connect to the time capsule, I can't even access time machine!
Usually I need to disconnect my Wifi, restart the Time Capsule, restart the iMac, and sometimes run Disk utility, then it will finally connect!
I've switched to a 5G network, deleted the files on my Time Capsule, started the downloads all over again, yet this still appears! Also this can happen after I do a simple restart on the iMac. Makes me not want to boot into Windows 7 anymore! I'm tired of this song and dance each time!
Next time it happens I'm going to give Apple a call and see if I really need to get the Time Capsule replaced!
I really don't want to do that again!
One further note, I've never had this happen with my Mac Mini that also shares the network and Time Capsule, it's my Home theatre machine and only sees use a few times a year... It has never had a failed backup!