Error database after installing membership plugin

I've just installed a brand new site.

The first plugin is WPMU Dev Dashboard.

The second is the membership plugin.

I installed the membership plugin via the WPMU Dashboard. It gave me an error message: "Error Database Connection".

I could not log in WordPress, so I deleted the plugin via cPanel. Then my site went back to life again. I tried installing the plugin again, the same problem occurred.

I installed another plugin via the WPMU dashboard, it was OK.

So, could you please check the current version of Membership plugin with WPMU Dashboard?

Many thanks,