I am using ubuntu 12.04 and my video card is ATI Radeon 5000. I cannot use double screen (extended version). I get this error

The selected configuration for displays could not be applied requested position/size for CRTC 148 is outside the allowed limit: position=(1280, 0), >size=(1280, 768), maximum=(1440, 1440)

I tried all display settings but it does not work.

Some outputs from the system settings:

root@ubuntu:~# lshw -C display
  *-display               
       description: VGA compatible controller
       product: Madison [Radeon HD 5000M Series]
       vendor: Hynix Semiconductor (Hyundai Electronics)
       physical id: 0
       bus info: pci@0000:01:00.0
       version: 00
       width: 64 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=fglrx_pci latency=0
       resources: irq:46 memory:e0000000-efffffff memory:f0020000-f003ffff ioport:d000(size=256) memory:f0000000-f001ffff
root@ubuntu:~# aticonfig --initial 
Uninitialised file found, configuring.
Using /etc/X11/xorg.conf
Saving back-up to /etc/X11/xorg.conf.original-0
root@ubuntu:~# cat /etc/X11/xorg.conf
Section "ServerLayout"
    Identifier     "aticonfig Layout"
    Screen      0  "aticonfig-Screen[0]-0" 0 0
EndSection

Section "Module"
    Load  "glx"
EndSection

Section "Monitor"
    Identifier   "aticonfig-Monitor[0]-0"
    Option      "VendorName" "ATI Proprietary Driver"
    Option      "ModelName" "Generic Autodetecting Monitor"
    Option      "DPMS" "true"
EndSection

Section "Device"
    Identifier  "aticonfig-Device[0]-0"
    Driver      "fglrx"
    BusID       "PCI:1:0:0"
EndSection

Section "Screen"
    Identifier "Default Screen"
    DefaultDepth     24
EndSection

Section "Screen"
    Identifier "aticonfig-Screen[0]-0"
    Device     "aticonfig-Device[0]-0"
    Monitor    "aticonfig-Monitor[0]-0"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection

I would appreciate any suggestions how to solve the problem. Thank you