Did you modify --- MAX-fileformats.txt --- in the cycling 74 folder??? That's the only reason I can think of. You should have a line that says...

max fileformat .wav WAVE;

nope that text is there ok. I reinstalled MAX MSP and restarted. it still wont respond after a "types WAVE" message, though if i send "types" message alone it will recognize waves

strange, it worked only a few days ago

Hrmmmmmmmmmmm. Yeah, that behavior is strange. I just tried it out with types WAVE and just plain old types and both dropped down alright. Sucky situation, I can't imagine why it would do that.... but, as they say.. .when in doubt, reinstall everything =/