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

<code>
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</code>

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