Yeah, double check the brace height to make sure it's right......Then, open your stance up a little bit. What I mean by that is for a right handed shooter, take a half step away from your body w/ your right foot. That will change the angle enough to probably avoid that......If that doesn't work, check your grip on the bow. Another thing would be to check the draw length, make sure it isn't longer.....And if it's the same as before, make sure it isn't too long for you.

If all else fails, try installing an STS system. This will stop the string as soon as it hits brace, and not smacking your arm.

If it wasn't doing this before you put on new strings, something is wrong w/ the installation I would suspect.