Make a global account

This option was removed in the latest version. Now users with the "post to twitter" permission have to select the twitter account to post to from a drop-down list.

By default twitter module try to add a different twitter account to each drupal user so if you try to add a single twitter acount to all drupal user
you need to do this steps:

1- Check all the installation process for a single account work.

(http://drupal.org/node/1346824)

2- Go to permission (admin/people/permissions) and check this options:

-Add Twitter accounts

-Use the site global Twitter account

-Assign a Twitter account as the site global account.

3- go to a account and add the twitter account, then will appear a option to do this twitter account global check and save this option.

4- add the global twitter account to each user.