Header already sent

Hello,

We have an issue with the plugin: “The plugin generated 2 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin. https://puu.sh/o6LCl/9fb3babbdb.png

If activated we cannot login and the front end is broken
If deactivated everything works ok
Please advise.

Thanks

https://www.ads-software.com/plugins/meks-flexible-shortcodes/