HELP Can't log on to AIM through my Blackberry Curve!!!?

I use AT&T - and have a data plan. I downloaded OZ AIM Instant Messaging but every time I try and log on I get a message that says

" Communication Failure. Please try again or check your settings."

I go to my applications and make sure to allow all communication to go through in my settings but still get the same result. Ive tried re-downloading, turning my phone on and off and its still the same. Can anyone help?