Your video card does not have enough video RAM to run with a shadow size of 8192 with full anti-aliasing (note, 8x anti-aliasing with a shadow texture size of 8192 requires a full 2GB of video RAM all by itself). Your card would need more than 4GB of RAM to do so.
Reduce the shadow texture size. If you are running with environmental mapping enabled, and full anti-aliasing, set the texture size to 1024. That should help.