Capturing video with one video card works but it get failed with another
 

I am capturing the display memory using frame buffer IOCTL and mmap. After capturing the display buffer i am sending it to some other computers.The display is perfect at other computer if the data graber computer uses cirrus Logic GD544x . My problem is that the display get distorted ( at the top)if I use Intel 845 or Intel 865 video card.Display setting is correct in both the cases. What is the reason and what can be the solution to this problem as I suppose that reading frame buffer memory is independent of video card.