When I checked the altex exchange market link from the OP it doesn't go to a bitcoin market. Altex might have removed that market and moved mint into the litecoin markets.

http://altex.ws/Market/?Pair=MINT/BTC

This link for a MINT/LTC altex market works. The MINT/BTC altex link in the OP should be replaced with this one if there's no altex bitcoin market any longer.

http://altex.ws/Market/Trade/?Pair=MINT/LTC