Error message when enable plugin

Hello,

I purchased this plugin and whenever I enable it is shows the message below either at Purchase button on single product page. Cache is already cleared after activation.

Warning: Illegal string offset ‘default’ in /homepages/46/d721678889/htdocs/winepig/wp-content/plugins/woo-free-shipping-bar/woo-free-shipping-bar.php on line 270 Warning: Illegal string offset \’default\’ in /homepages/46/d721678889/htdocs/winepig/wp-content/plugins/woo-free-shipping-bar/woo-free-shipping-bar.php on line 270 Warning: Illegal string offset \\\’default\\\’ in /homepages/46/d721678889/htdocs/winepig/wp-content/plugins/woo-free-shipping-bar/woo-free-shipping-bar.php on line 270 You have purchased £59.99 of £100.00

Thanks in advance,
Jozsef