There are no drivers or issues reported for the projector on Mountain Lion, what USB driver did you install? When was the last time the projector was used?
Have you tried a different USB cable and a different USB port on the computer?
Sometimes the driver that comes with the projector is not the last version, look at the Epson Website the driver for the model of you projector, download and install it; this may correct the problem. I did the same and it works.
One else, set your projector with Extended\USB Type B\USB Display