Do you use Twitter Tools on your blog to autopost your new posts, or to show a daily record of all your tweets?
Did is suddenly stop working yesterday?
Unfortunately twitter removed the end points which the plugin spoke to. They did announce this would be happening over a year ago, and have since even released a new version of their API.
Whilst you are waiting for an official fix, you can make this small change to the plugin code to sort it now.

In WordPress admin go to Plugins, Editor, select Twitter Tools from the drop down.
In the code box find

define('AKTT_API_POST_STATUS', 'http://twitter.com/statuses/update.json');
define('AKTT_API_USER_TIMELINE', 'http://twitter.com/statuses/user_timeline.json');
define('AKTT_API_STATUS_SHOW', 'http://twitter.com/statuses/show/###ID###.json');

and replace with

define('AKTT_API_POST_STATUS', 'https://api.twitter.com/1.1/statuses/update.json');
define('AKTT_API_USER_TIMELINE', 'https://api.twitter.com/1.1/statuses/user_timeline.json');
define('AKTT_API_STATUS_SHOW', 'https://api.twitter.com/1.1/statuses/show.json?id=###ID###');

Then hit the Update File button.