RFM12B only sends messages and do not receive anything

Hey, I currently bought 2 RFM12B chips, solder the resistors and connected it (instruction), one to an Arduino UNO and one to an Arduino Mega1280. Then I used the simple test sketch to check if it's all working. But a few problems came up: The Arduino, no matter which of them, only transmits if the IRQ Pin (2) is not connected. If I remove Pin 2 the TX LED turns on everytime something is send (feedback via Serial Monitor). But the other Arduino doesn't capture anything. I tried both as receiver and transmitter(using Pin2 and not) -> both do not receive anything and both just sending something when Pin 2 is removed. Where is the mistake?