Nickvdp on "[Plugin: Share Buttons by AddThis] Twitter button not working: An unknown error occurred. Yikes! Please try again."

I have successfully installed the AddThis plugin. Everything's working fine except the Twitter share button. When I click it, it throws an error: "An unknown error occurred. Yikes! Please try again."

Any Idea's what might be causing this?

Example URL: http://www.kvacreditfinance.com/zorg-dat-een-garantieverklaring-zekerheid-biedt-en-geen-kat-in-de-zak-wordt/

I'm running WP 3.6.1 & AddThis 3.5.3

http://wordpress.org/plugins/addthis/