Very nice template...

When I click the "checkout" button (either from the cart or the button in the top menu) I get a "white" screen. Any ideas on what this might be?

Zen Cart 1.3.8a
Database Patch Level: 1.3.8
v1.3.8 [2008-12-08 05:55:24] (Fresh Installation)
v1.3.8 [2008-12-08 05:55:24] (Fresh Installation)