I have the (delightful) misfortune of having 3 graphics cards. They are XFX Radeon 5750s. Each drives 2 monitors via dvi. I am having a really hard time getting these running on fedora 15 (gnome 3). So my setup is 3 columns of 2 monitors (the upper monitor is mounted upside down in each column to reduce the bezel between monitors).

When the (graphical) login screen comes up all 6 have the blue stripey background that must be the default, but then when I login, things get interesting.

In the xorg.conf below, you will see only 2 of the screens in the serverlayout while the other 4 are commented out. Logging in with only 2 of the screens active works well (and it even remembers that the top one is upside down, and should be considered above the lower, i am not sure where it stores this info, but i set it using the graphical "Displays" settings)

However, as soon as I uncomment a third screen, or more, it gives me an error message when I login. It's one of those friendly, less helpful messages (Oh no! Something has gone wrong. A problem has occurred and the system can't recover. Please log out and try again).

If i do not use an xorg.conf, then the "Displays" prefs pane shows only the two monitors on one of my graphics cards

Thanks to anyone who can help me get going! (xorg.conf and then lspci below, and xorg log)

xorg.conf

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen        "Screen0" 0 0
    Screen        "Screen1" Below "Screen0"
#    Screen        "Screen2" RightOf "Screen0"
#    Screen        "Screen3" RightOf "Screen1"
#    Screen        "Screen4" RightOf "Screen3"
#    Screen        "Screen5" RightOf "Screen4"
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
    ModulePath   "/usr/lib/xorg/modules"
    FontPath     "catalogue:/etc/X11/fontpath.d"
    FontPath     "built-ins"
EndSection

Section "Module"
    Load  "record"
    Load  "dri"
    Load  "dbe"
    Load  "extmod"
    Load  "dri2"
    Load  "glx"
EndSection

Section "InputDevice"
    Identifier  "Keyboard0"
    Driver      "kbd"
EndSection

Section "InputDevice"
    Identifier  "Mouse0"
    Driver      "mouse"
    Option        "Protocol" "auto"
    Option        "Device" "/dev/input/mice"
    Option        "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
    Identifier   "Monitor0"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor1"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor2"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor3"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor4"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor5"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection


Section "Device"
    Identifier  "Card0"
    Driver      "radeon"
    BusID       "PCI:4:0:0"
EndSection

Section "Device"
    Identifier  "Card1"
    Driver      "radeon"
    BusID       "PCI:5:0:0"
EndSection

Section "Device"
    Identifier  "Card2"
    Driver      "radeon"
    BusID       "PCI:6:0:0"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device     "Card0"
    Monitor    "Monitor0"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "Screen1"
    Device     "Card0"
    Monitor    "Monitor1"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "Screen2"
    Device     "Card1"
    Monitor    "Monitor2"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "Screen3"
    Device     "Card1"
    Monitor    "Monitor3"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "Screen4"
    Device     "Card2"
    Monitor    "Monitor4"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

Section "Screen"
    Identifier "Screen5"
    Device     "Card2"
    Monitor    "Monitor5"
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

lspci output follows

[tgm@tgm ~]$ lspci
00:00.0 Host bridge: Intel Corporation 5520/5500/X58 I/O Hub to ESI Port (rev 13)
00:01.0 PCI bridge: Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port 1 (rev 13)
00:03.0 PCI bridge: Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port 3 (rev 13)
00:07.0 PCI bridge: Intel Corporation 5520/5500/X58 I/O Hub PCI Express Root Port 7 (rev 13)
00:14.0 PIC: Intel Corporation 5520/5500/X58 I/O Hub System Management Registers (rev 13)
00:14.1 PIC: Intel Corporation 5520/5500/X58 I/O Hub GPIO and Scratch Pad Registers (rev 13)
00:14.2 PIC: Intel Corporation 5520/5500/X58 I/O Hub Control Status and RAS Registers (rev 13)
00:14.3 PIC: Intel Corporation 5520/5500/X58 I/O Hub Throttle Registers (rev 13)
00:1a.0 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #4
00:1a.1 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #5
00:1a.2 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #6
00:1a.7 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB2 EHCI Controller #2
00:1b.0 Audio device: Intel Corporation 82801JI (ICH10 Family) HD Audio Controller
00:1c.0 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Root Port 1
00:1c.1 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Port 2
00:1c.2 PCI bridge: Intel Corporation 82801JI (ICH10 Family) PCI Express Root Port 3
00:1d.0 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #1
00:1d.1 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #2
00:1d.2 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB UHCI Controller #3
00:1d.7 USB Controller: Intel Corporation 82801JI (ICH10 Family) USB2 EHCI Controller #1
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)
00:1f.0 ISA bridge: Intel Corporation 82801JIR (ICH10R) LPC Interface Controller
00:1f.2 IDE interface: Intel Corporation 82801JI (ICH10 Family) 4 port SATA IDE Controller #1
00:1f.3 SMBus: Intel Corporation 82801JI (ICH10 Family) SMBus Controller
00:1f.5 IDE interface: Intel Corporation 82801JI (ICH10 Family) 2 port SATA IDE Controller #2
02:00.0 PCI bridge: nVidia Corporation NF200 PCIe 2.0 switch for mainboards (rev a3)
03:00.0 PCI bridge: nVidia Corporation NF200 PCIe 2.0 switch for mainboards (rev a3)
03:02.0 PCI bridge: nVidia Corporation NF200 PCIe 2.0 switch for mainboards (rev a3)
04:00.0 VGA compatible controller: ATI Technologies Inc Juniper [Radeon HD 5750 Series]
04:00.1 Audio device: ATI Technologies Inc Juniper HDMI Audio [Radeon HD 5700 Series]
05:00.0 VGA compatible controller: ATI Technologies Inc Juniper [Radeon HD 5750 Series]
05:00.1 Audio device: ATI Technologies Inc Juniper HDMI Audio [Radeon HD 5700 Series]
06:00.0 VGA compatible controller: ATI Technologies Inc Juniper [Radeon HD 5750 Series]
06:00.1 Audio device: ATI Technologies Inc Juniper HDMI Audio [Radeon HD 5700 Series]
07:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 02)
08:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 02)

xorg log (posted to fpaste due to how long it is. thanks to marcusw for the request)

http://www.fpaste.org/r5ww/

xorg log with all 6 monitors enabled in xorg.conf (they all turn on and have blue, but then one gets the aforementioned user-friendly error message). http://www.fpaste.org/X63H/