Doesn't work in 3.9.1 with some WP themes

When I installed with one them it destroy layout and makes such error: “Meggings next level yr, 90’s small batch four loko brunch wes anderson fixie american apparel flexitarian pitchfork neutra. Constructed in cotton sweat fabric, this lovely piece, lacus eu mattis auctor, dolor lectus venenatis nulla, at tristique eros sem vel ante. Sed leo enim, iaculis ornare tristique non, vulputate sit amet ante. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Aenean fringilla laoreet mauris lectus pellentesque eu.”

https://wordpress.org/plugins/readykommerce-multi-newsletter-signup-light/