First check if you inadvertently altered the color depth of your display while installing the new driver and configuring things with sax2. Have a look at the files /etc/X11/XF86Config and /var/log/XFree86.0.log. If your code can't handle different color depth, you will surely run into some problems with regard to ZPixmap. See "Xlib Programming Manual Vol. 1" and "Xlib Reference Manual, Vol. 2", by Adrian Nye, O'Reilly, for a detailed discussion.
Hope this will help.