How are the radios powered. One of the biggest problems with using the rf24 radios is trying to power them from the weak 3.3V regulator on Arduino boards. They just can't supply the required current. A 10uF (or larger) across the rf24 power input (as close to the rf24 as possible) will sometimes help. I use a separate LM1117 3.3 regulator for my radios. There are adapters available that have the regulator and other components on board to power the radios.
I used Robin2's simple rf24 tutorial
to get my radios to work. There is also information on powering the radios in the tutorial.