Not working

I have install and activate your prlugin . After that I have got this erro in header.

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /wp-content/plugins/croatian-shipping-for-woocommerce/croatian_shipping_for_woocommerce.php:1) in /wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

https://wordpress.org/plugins/croatian-shipping-for-woocommerce/