create a new blog template to keep consistancy among blogs?

Hi, I have a multisite using marketpress and have installed Marketpress front end. I am able to create a store and see the front end if I create it as the site administrator. However, I had my friend try to create a site without a login from scratch and he was taken to a blank page instead of an add products page. I did some reading on the Front End site and thought adding a new blog template (through my admin dashboard) was the solution. I have attempted to create a new site to be used as the template, but I keep getting this error message

Whoops! The blog ID you posted is incorrect. You cannot template the main site. Please go back and try again. (Generated by New Blog Templates)

Would appreciate any help!