I would make sure the 'drain hole' is clear and not stopped up. Sounds like it could be stopped up and you have so much water in the unit it's over-flowing and coming out inside the window.

hope this helps.

p.s. one other thing - you might need to put another hole in the unit (to allow better draining). Typically these units just drip water outside and putting (with a drill) another hole in the bottom of the unit to allow better draining is easily done.