COD Ghosts Directx problem

Hi. I play games such as COD on Windows 7 accessed via bootcamp on my Mac. No problem with COD except for COD Ghosts, the latest. The games install okay but shows 'irrecoverable error with Directx' . I have uninstalled and reinstalled the game and run the Directx diagnostic which shows all okay. The graphics card is AMD 4850. Any help please?

Here are the System Requirements:

CPU: Intel Core 2 Duo E8200 2.66 GHZ / AMD Phenom X3 8750 2.4 GHZ or better
CPU Speed: Info
RAM: 6 GB
OS: Windows 7 64-Bit / Windows 8 64-Bit
Video Card: NVIDIA GeForce GTS 450 / ATI Radeon HD 5870 or better
Sound Card: Yes
Free Disk Space: 40 GB

Also, you can go to this web site and click on "Can I run COD Ghosts" and let it analyze your machine. I suspect your video card is the problem. Here's the LINK.

Thanks for this. Cheers.