This plugin is essentially unmaintained. If you have it installed and configured, it will probably keep on working for a while.
Twitter changed the way accounts are used inside the JavaScript widget. And I am quite tired of wasting time chasing the whims of a company like Twitter.
(I should have thought of that earlier).
Anyway, you shouldn't use this type of widget anymore. This type of third-party JavaScript is often blocked by browsers and users, so many people will not see it.
If you want to have a Twitter Feed on your website, you are better off with something that is done serverside in PHP.
There are probably many plugins that offer that functionality.
A Twitter Widget that is easy to configure and easy to style. It uses the Embedded Timeline Widget of
Twitter.com.
You can have it load an extra stylesheet, where you can style the layout of the widget.