blue tooth ipad iphone connection

I cannot connect my iPad to my iPhone 4 via bluetooth anymore. At one stage months ago it was possible. so help, please! The iphone is a 4 model MC605B/A with version 6.1.3 software; the ipad is model MC705B/A also running software version 6.1.3. On both devices the other device is visible when the bluetooth is set to "on" but when the name of the device is tapped to connect the error message "Connectin unsuccessful. make sure iphone is turned on and in range". The devices are placed next to one another. I have powered down both devices but stil the same issues.