As most people have said, CO2 isn't good for electro guns.
This because of two main reasons:
1. CO2 is a dirty gas, eg. unlike air which is filtered while being compressed as its main use is for breathing apparatus, CO2 isn't filtered during compression.
2. When CO2 is compressed it turns into it's liquid form. This can mean at high rates of fire that liquid is drawn in to you gun. This can damage O rings and solenoids either causing you to have to maintain you gun a lot more or potentially screw your gun up. While anti shipons can be fitted to CO2 tanks to minimize this they aren't 100% effective.
As Devrij has stated when CO2 turns back to a gaseous state it has a cooling effect, and can cause your gun to freeze, can still remember my first mag freezing up due to CO2, not a pleasant experience.
IMO buy yourself a preset air tank (have a look on the for sales threads).
Hope this helps and explains it a bit more.
Matt