multiple video cards error

[truename]

There are four PCI video cards on the mainboard. They are the same with each other. I have written the driver myself running in XFree86 4.2.0. The four video cards work fine in Redhat 7.0 when setting "xinerama" in the config file. 
Then I upgrade the driver in order to run in Xorg 1.6.4. The new driver can only make the primary video card work fine in Ubuntu 9.10(XServer version is 1.6.4) . But it cannot make four video cards work fine at the same time when setting "xinerama" in the config file. In the log I find that it can read rom of the primary video card. But it cannot read roms of the other video cards. The Xserver reports an error:
Cannot read V_BIOS (3) Input/output error
The driver cannot read or write I/O ports except the primary video card.
Any comments on this question would be appreciated.
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