Calling C# functions with action script 3.0

Hi I am trying to code a system where when a user enters my swf file (My actionscript 3.0 game compiled) it calles a c# method OnEnter() this method updates the users online column in the database to 1 and when they leave the game it calles OnLeave() this method sets the online to 0 if the c# application is not open then it will show a black screen and display a message "Server is not open"