While trying to install CentOS 6.4 IN DUAL BOOT with win 7 there was this error "sda must have gpt label". I don't know how to fix it and I also don't want to repartition my hard drive.
Disable UEFI in BIOS (manual) or create a GPT partiition table (
Example of creating one from Arch wiki:
# gdisk /dev/sdX
o # create new empty GUID partition table
n # partition 1 [enter], from beginning [enter], to 100GiB [+100GiB], linux fs type [enter]
n # partition 2 [enter], from beginning [enter], to 108GiB [+8GiB], linux swap 
w # write table to disk and exit
Another option is to use
parted utility during installation. Inject "CTRL+ALT+F2" during your installation process to go on command line with 'parted' utility.
then return to installation process with CTRL+ALT+F1.