I have reconfigured my airport time machine as an extension of my wifi network... now I am not able to use it as a backup device?

After setting up my wifi with a new Airport Extreme as a base unit with 2 Airport express units I decided to reconfigure my Airport time capsule as an extension also. I was able to do that but now I can't access my backup data on the time capsule. When trying to use it as a backup I get the message to see my Administrator.... I am the only user and the administrator of my iMac....