It appears that Twitter is denying access to the resource requested by your server. I don't think this is a XenForo issue but rather an authorization issue from Twitter.
How do you go about integrating Twitter into your widget?
Have you created an API on Twitter developer website ?
@nicodak thanks! It was actually a plugin I had on wordpress called "Wordfence" I had to disable it. I will have to figure out later how to "re-enable" it to protect WP while allowing me to use the Twitter Feed on XF.