Marketpress [contributor,editor] access

Hi,

I am trying to setup a toned-down Etsy site. I want to offer store accounts to people who wish to upgrade their free account to a store account. By default, a user will be assigned Subscriber privileges and an upgrade will promote them to either Contributor or Author status. How can I enable "Product" menu for Authors and Contributors? I tried using the "Widget Logic" plugin to configure marketpress menu access. I continue to get "You do not have sufficient permissions to access this page." How can I work around this permission issue?

Chris