Why are you so lucky?
I wish my birthday was every day, too!
How can I set that up?
It's probably a change that you have made to that event in iCal... You should check that event. It may help to delete your birthday event completely, then re-sync to your Touch.
If that's the only event where you have problems, I will go out on a limb, and say that you really don't need to remember your own birthday, do you?