Solution:
You are light years behind. Why are you still using wordpress 3.0.1.
Your problem is not with the plugin, but with your wordpress version. get_submit_button() was introduced in wordpress 3.1. This is what is triggering the fatal error, as this function doesn’t exist before 3.1
You should really really really upgrade your wordpress install. You are seriously missing out on some of wordpress best features. UPGRADE TODAY!!!!