wrong usage of t()

error message during translation:
The first parameter to t() should be a literal string. There should be no variables, concatenation, constants or other non-literal strings there. At t('Users with the role '.$role.', will have the ability to create users with these roles.') in user_creator.module in line 89. Read more at http://drupal.org/node/322732
With this error the necessary strings are not extracted for translation.

Replace

 t('Users with the role <em>'. $role .'</em>, will have the ability to create users with these roles.')

by

 t('Users with the role <em>@role</em>, will have the ability to create users with these roles.', array('@role' => $role))

Additional hints in order to ease translation:

• Do not split sentences into different t() functions.
• Always use the mentioned structure for texts with variable content.