If you used rezinject properly (not forgetting to delete old file and rename rezNew to rez), and you are getting an error or some other 'hiccup'. Try entering CA again and again. If after 3 tries you still can't start CA, try restarting computer. If that doesn't work talk to the mod maker, post in the thread you found the mod in.
I'm currently trying to mod a gun into the new M417 SB. I have it looking like the M417 SB, but I'm still tweeking it. The point is, It took me 3 tries to start CA so I could see the mod working.