On June 11, 2013 , Twitter has changed his API from version 1.0 to 1.1 . In version 1.1 there are new features, but also users will need to create their own Twitter API keys.
Twitter API keys are required for:
1. Integrated Twitter feed
2. Twitter social counter
3. Twitter widget

Without Twitter API key listed functionalities will not work.

Getting Twitter API keys is easy:
1. Go to https://dev.twitter.com/apps/new .
2. If you are already logged in your Twitter account you will be automatically redirected to the step 3. If you are not logged in, then enter your Twitter username and password.
3. In this form you will need to enter basic information about your Twitter app:
– Name: Your application name. Example: MyNewWebsite
– Description: Application description which will provide more details. Example: Tweeter feeds for MyNewWebsite
– Website: Website where your Twitter application will be used. Please note that you should enter website URL with http:// or https:// . Example: http://www.mynewwebsite.com

create-application
– Return URL: Where application should return you after successful login. Not required. Example: www.mynewwebsite.com/welcome
4. Read and agree with “Agreement”, enter captcha and hit “Create your Twitter application”
5. On this page Twitter will display your keys. Now you should hit “Create my access token”. Without token your Twitter feed will not work.
6. After redirect back to the same page click on tab “OAuth tool”. Under this tab you will find your consumer key, consumer secret, access token and access token secret.

oauth
7. In new tab/window login into your WordPress website, and go to “Social” tab under theme panel.
8. Enter your Twitter authentication keys in the proper fields and save changes.

enter-tw-keys
9. You are done!

Twitter feed, social counter and widget should be working now.