Direct from the website:
Lehigh ID card holders (students, faculty & staff) are admitted free to all home Athletics events, with the following exceptions: Home Football vs. Lafayette, Home Basketball vs. Lafayette, Home Wrestling vs. Penn State, and other Summit Series events added prior to a given season. Lehigh ID card holders are not admitted free to postseason events, such as EIWA Championships, NCAA Football or PAtriot League Basketball.
I think it is pretty poor form by the Athletic Department to charge students, even just for certain high profile games.
Just realized as well that the Lehigh valley Hoop Group Showcase high school event is today, so that may effect attendance a bit as it gives local hoop fans a very good alternative to see some quality hoop.