Cannot Register for Event if i set $0 price for members in WP-Admin

I have been using Membership Pro addon with Event plugin so i can set different prices for members to register for same event.

I created an event and i set $0 price for members and other price for non members.

problem is members could not register for an event but non member can register because that price is not 0 .

if i set the more than $0 price then i can register only otherwise not.....

please help asap..................