I've been struggling with some code that was failing to "begin()" any devices on my i2c bus. I've uploaded a scanner program from arduino playground which lists the addresses of any i2c modules found. With a single sensor connected the whole arduino freezes but when I unplug the wires from the a4 and a5 pins it continues. Plug them back on and it locks. I've tried with the SDA / SCL wires reversed as I've seen mention of things being backward.
Anyone know what I'm missing?