The $string argument to t() should not begin or end with a space
The correct way of using variables in t() function is using placeholders. 

Example of a correct usage:

$string = t('Role Limit @value', array('@value' =&gt; $value));


There are three types of placeholders for t() function.


@variable : The variable will be checked through check_plain() function before it is inserted, so you don't need to check it in your script.
!variable : The variable will be inserted as it is.
%variable : The variable will be checked through check_plain() and highlighted with drupal_placeholder()