Problem

Twitter widgets are no longer displaying in IE7 or IE8. Instead, you will only see Loading Widget #123456789

Cause

In late 2014, Twitter removed support for widgets in Internet Explorer 7. In January 2015, they removed support for Internet Explorer 8 as well.

For more information see this announcement from Twitter.

Resolution

The only available resolution is to use a browser that is supported by Twitter.

See  this page for supported browsers.