Users typically receive a "0xC0000004 Divide by Zero" exception.

You needed KB841999 if:

KB841999 is a perfect example of a targeted compatibility update —a small, critical fix for a specific problem affecting a minority of users. It solved the "4K sector misalignment" issue for Windows XP x64 Edition, ensuring that enterprise and technical users could deploy large-capacity hard drives without performance loss or data risk.