Another thing that it is important to get right is what injector you use and how you use it.
As it happens our very own Eminem has made as entire thread about this already which can be found here:
I would recommend AirDrop as it is my personal favourite.
Hacks Vs Antivirus
A problem that can occur often is that your antivirus software detects that hack you are trying to use as a threat to your computer.
It will therefore it will stop your hack form working and more then likely, crash CA.
Now there's not much you can do about this except temporarily disable your AV while you inject the hack and CA starts up.
Some hacks and .rez edits can actually corrupt some of the game files CA need in order to run.
When this happens there's nothing you can do except re-download and re-install CA - Game client/patches page