can't access old time capsule backups

My time capsule kept saying failed to backup.

I restarted it and then it started backup normally again but, when I ener time machine I can only see back ups that are up to a month old when I should have close to two years!!

this happens randomly where I try to access them and cant, but later i try again and can access everything

what could cause this?

some info

Time capsule 1st gen 1TB

macbook pro 15 inch early 2011 OSX 10.8.2