|I'd like to but||...I'm meeting a friend|
|I'd love to but||...I'm really busy this weekend|
|Ah, no.. sorry||...I've got to meet a friend|
|Maybe another time?|
Maybe next time?
I really appreciate the invitation (or 'invite')
I can't make it
From: BBC Learning English - http://www.bbc.co.uk/worldservice/learningenglish/