Half Life 2: Ep2 Error??

I just bought The Orange Box a couple days ago. All of the games on it run great except HL2:Ep2. I start the game and it runs perfect up until a very specific point. The little shack area where Alyx contacts her dad is where the problem takes place. They talk for a bit and when the doctor says, "combine portal," the word portal will loop about 4 times then a message saying ," The instruction at 0x12438f3f referred memory at 0x0e2bf3c0. The memory could not be read."

I have Updated windows, all video/sound drivers, and my processor, but the problem continues. I have also reinstalled the game and steam itself.:banghead

Any help would be great!