I had the same problem 2 weeks ago...I couldn't even save it to the hard drive.
I took the disc to my local Game Crazy...they cleaned it...and thank god I could save it to my hard drive....no problems since as I only play it off the HD. Try saving it to the HD...and if it keeps freezing at the same spot...then go get it cleaned. Somehow my disc had a small scratch/blemish in it.