RGFormsModel::get_lead_count()

I'm trying to figure out a way to count the number of times a logged in user has submitted a form.

Searching the forum I came across WPSpecialits post and Marsius's post regarding:
the get_lead_count function.

I just can't get it to work.

Here's what I've tried:

if (is_user_logged_in()){
  $user_info = get_userdata( $current_user->ID); //this bit works and pulls the user id.
$entry_count = RGFormsModel :: get_lead_count( $form_id, $user_info->user_login); //This bit doesn't work - if i echo $entry_count i get nothing!!