how can I re programme my ford focus key fob?

Hi when I bought my Focus 10 months ago there were two keys but only one with electronic fob. so I bought a fob online and using the method in the manual I reprogrammed it first time.But now it has stopped working tried to re programme it but no good. After trying, neither key will work even though I got both bleeps.is there a limited number of times that you are allowed? HELP!!!