WP_Error in Simple Invite Code

Hello again,

I'm getting this error when I enter an invalid sign up code:

Fatal error: Cannot use object of type WP_Error as array.

Here is the line it references:

$error[] = __('You need to enter an invite code in order to register.','membership');

I've tried:

$error = __('You need to enter an invite code in order to register.','membership');

and:

$error->__('You need to enter an invite code in order to register.','membership');

Both to no avail. Anyone experience this before?

Thanks,

Owen