Fatal error: Call to a member function get_error_message() on a non-object in /home/*****/public_htm

I have two issues or questions that I need some help with.

The first is a Fatal error: Call to a member function get error message () on a non object message that is showing up on my registration page for the membership plugin. I just upgraded to the newest version and it corrected an error from the previous plugin version but now I get that error message and have no idea how to fix. See the screen shot of the error.

I am using a Wootheme (Strata) theme with the newest version of the membership plugin. It is not network enabled as I need to selectively use the membership plugin for sites that have paid for access to that upgrade. It is enabled for this site and has been setup.

The second applies to the membership plugin as well. One of the setup items is to disable Wordpress's standard registration. The forums give a help answer for a multi-user site and a standard site. The problem is that I need to be able to disable the registration ONLY on the sites that use the plugin for membership not the entire network. Because it was setup as a multi-user system I only have the only of disabling in the Network settings which disables the registration for all sites. How do I disable the registration for only the one site in a multi-user environment?