At least from what I've seen, it appears that you don't have an “else if” clause, so I'm thinking “NEDM”.

HAI
CAN HAS STDIO?
PLZ OPEN FILE "LOLCATS.TXT"?
	AWSUM THX
		VISIBLE FILE
        NEDM PLZ OPEN FILE "LOLCATS.DAT"?
              VISIBLE FILE
	O NOES
		INVISIBLE "ERROR!"
KTHXBYE

See: http://lolcode.com/contributions/o-rly — Tetraboy, 2007/05/30 17:32