Can't get two way communication with nRF24L01

Projects Networking, Protocols, and Devices
1

I've tried all sorts of combinations of software and hardware configurations, but I can't get: Arduino2 to send information back to Arduino1. In every case that I've tried, Device1 can send and Device2 can receive, but not the other way around.

Arduino1: Arduino Mega2560 using nRF24L01 soldered 10uf capacitor
Arduino2: Arduino Mega2560 using nRF24L01 soldered 10uf capacitor

I've tried my own custom programs.
I've tried the following sketches compiled/built/uploaded through Eclipse and the Arduino IDE:
https://github.com/stanleyseow/RF24/blob/master/examples/nRF24_Serial_Chat/nRF24_Serial_Chat.ino
http://maniacbug.github.io/RF24/pingpair_8pde-example.html
I've tried 4 different radios(all with the 10uf capacitor) swapped between the two Megas.
I've tried different CS and CE pins on both Arduinos.
I've even tried swapping the wires between the two devices!

I've turned on SERIAL_DEBUG inside of the RF24 library and I've found that it's timing out on receiving the ACKPacket since I can see that tx_fail == 1 in RF24::write().

What does this mean, Arduino2 has a bad MOSI pin? MISO on Arduino2 must be working because I can receive the data from Arduino1.

2

Well this is a pretty nasty problem to have on a brand new Arduino, but it looks like it's bad. I got a third and fourth Arduino from a friend and they both work great with each other and Device 1 with different radio configurations. Device 2 can transmit to all devices, but it can't receive from any.