Scroll bars - Painting in a window

IDE : VC5

I am creating a window  control inside a dialog and drawing horizontal and vertical lines inside that to make it as a grid control.

The window has horizontal and vertical scrool bars and I am handling these scroll events and repainting the uncovered area to show rest of the grid.

In windows NT, when horizontal scroll bar is used the grid is not repainted in the area newly made visible.

But It is working perfectly in windows 2000.
Is the difference in MSVCrt,MSVCirt,MFC42,GDI32 dlls in these OS   can cause these problems?

The code is

GetClientRect(&rc);
ScrollWindow(iScrollPos,0,&rc,&rc);

Where iScrollPos is the value I am calculating to fix the number of columns to be moved.


While debugging The OnHScroll-scrollwindow calls onpaint and draws all the lines
but it is not displayed in the moved portion.


What could be the problem?

Either calling update window or passing rc = NULL is not solving it.

Regards.
Viswanath