Rainbowduino mega 2560 i2c problem. Neorainbowduino

Hello all.
I'm very new to the world of arduino and have gotten myself an Arduino mega 2560 as well as a rainbowduino and rgb matrix.
I am running the neorainbow firmware on both devices and am trying to communicate with the examples in the firmware package.
I have edited the wire libraries as stated here: Rainbowduino fun – aka neorainbowduino
And I hooked up everything so it appears correct.

When I run the 12c scanner it finds my rainbowduino!
When I load the simple example it runs showing random pixels on the matrix but I get some errors after a while as follows:

com.neophob.lib.rainbowduino.Rainbowduino waitForAck
INFO: No serial reply, duration: 30ms

When I run the invader example I get no display but the sketch runs without error in processing.

Anyone got any ideas? I've been scratching my head for over a week on this one.

I was wondering if there are any notable differences in the way a mega 2560 handles i2c compared to other arduinos. I know the pinout is different but is that all?

Power issues?

How are you powering all of this? Not off the Arduino I hope.

I have a Mega2560 and the I2C interface seems to work fine -- even with OneWire.

Power issues?

Shouldn't be. I'm running the rainbowduino off a 8.5v input.

I have the pins (sda, sdl, gnd, reset) hooked up from the arduino to the rainbowduino.