Problems with AMD graphics driver installation on Ubuntu 12.04

Problems with AMD graphics driver installation on Ubuntu 12.04

I installed Ubuntu 12.04 on my desktop with two screens, but one of the
screens has not been detected. As far as I understand the problem comes
from the wrong video card driver, so I followed the instructions to
install the video driver for Radeon HD2400. As a result I have the
following:
In system details I see that the graphics is VESA: RV610 (which is
correct), but the fglrxinfo command gives me the following:
X Error of failed request: BadRequest (invalid request code or no such
operation)
Major opcode of failed request: 153 (GLX)
Minor opcode of failed request: 19 (X_GLXQueryServerString)
Serial number of failed request: 12
Current serial number in output stream: 12
And when I try to launch Catalyst control centre I get:
There was a problem initializing Catalyst Control Center Linux edition. It
could be caused by the following.
There isn't any installed AMD graphics driver, or the AMD driver is not
functioning properly. Please install the AMD driver appropriate for you
AMD hardware, or configure using aticonfig.
In the additional drivers menu I see that "No proprietary drivers are in
use on this system."
How can I fix this?