I have this re-occurring problem in iCal.

A while back I recieved a meeting invite via mail for a meeting with client.
It lobbed itself into iCal and thats fine. But I have been trying to delete it becuase it gives me an annoying number 1 above its icon in the dock. Like I have a new email or something.
I delete it, but it keeps putting itself back there.

How do I get rid of it?