Gonzalo Ares wrote:
  

The error is:
kernel: PCI: BIOS Bug: MCFG area at e0000000 is not E820-reserved
The mainboard is a Asus p5q
The centos is: 5.3 (2.6.18-128.7.1.el5)
  
    

do you have the latest BIOS on that board?   looks like they have 
released several updates, latest being 2102 (assuming its the basic p5q 
and not one of hte innumerable proturbohyper++ versions)
.   This wouldn't be the first time an Asus board has had bad 
PCI/ACPI/etc data structures in its BIOS.

googling for that error indicates if you're running xen, its totally 
bogus, if you're running a regular kernel, its an indication of a BIOS 
problem, but it should have no impact on your system operation or 
performance.