Time Machine

Sorry to be back - I am not able to get my timemachine backup working. I noticed recently that since august sometime, my macbook had not backed up to the readynas. Luckily I have an Apple time capsule as well. I reset everything - then followed the instructions - ie set up a shared time machine with sufficient capacity (I need 1TB and set up 3TB) - user ID default ReadyNAS and password. I then went to time machine on my mac and added the disk, put in user ID (ReadyNAS) and password. All looks fine, but when time machine tries to backup to the NAS, it tries, then skips directly over to the time capsule as a second option. It used to work fine, so Im at a loss what to do. 

Thanks again for the prompt help - so far its been really great. J Rose

ps: it works fine still for my kids Mac Airs..