Default Email Problems Help!!!

I am trying to enter my ukonline email settings, but when ever it connects it comes up with;

"Messages cannot be downloaded to your mobile device, make sure you are connected and that your email account settings are correct"

I have put it as POp3, and pop3.ukonline.co.uk and the SMTP as smtp.o2.co.uk

any ideas what I am doing wrong?

your help is appreciated.

Andy