I am trying to get two nrf24l01 to work. they worked when I first got them and set them up. I used the "getting started" sketch from the rf24 lib. now I use the same sketch and one of them is acting very strangely. it prints the correct message and then stops but when I touch the arduinos icsp pins it starts receiving very quickly. I think that I may be shorting it to ground or something. is this the problem others have and require connecting a capacitor across the supply and ground on the rf24 board, something to do with the 3v supply being a bit noisy? not sure on this, please help thanks simon :)

The nRF24L01 module has its own decoupling capacitors on board.

Sounds like you have and issue with the SPI wiring - are the wires short and running together with a ground wire?

The module has 5V tolerant inputs, but the module supply must be 3.3V and it must provide enough current (can't recall but the on-board Arduino 3.3V pin may not provide enough for the module).

If the 3.3V rail wasn't holding up it could prevent the Arduino reading MISO pin since 3.3V is only just enough for reliable recognition by the 5V Arduino.