I have an ATI All-in-Wonder Pro, AGP OEM. It seems that I does not recognize the firmware version of my card (OEM) and it sends the wrong vRefresh Rate. (For example, if you set it at 80hz, the card will set the monitor to 40hz.) I have tried with other monitor drivers and monitors, and I have discarded the monitors as the source of the problem. RedHat 6.1 with the latest version of XFree86 and XF86_Mach64. It used to work with the RedHat 5.0 CD.
you are going to have to be much more specific, including the modeline that is in use, etc. etc.
closed due to lack of additional feedback. Please reopen if you have more pertinent information.