Code to Restrict multiple user login in axapta

I need help to get solution for following problem if you have idea then reply me your response.

I am using following code in info class

 void startupPost()  
 {  
 // To restrict user login form second login  
 xSession session;  
 SysClientSessions SysClientSessions;  
 UserId currentUserId;  
 int counter;  
 ;  
 currentUserId = curUserId();  
 if(currentUserId!="Admin")// Allow Admin User to login multiple time  
 {  
 while select SysClientSessions  
 where SysClientSessions.userId == currentUserId &&  
 SysClientSessions.Status == 1 // 1 : Login 0 : Logout  
 {  
 session = new xSession(SysClientSessions.SessionId, true);  
 if (session && session.userId())  
 {  
 counter++;  
 }  
 }  
 if(counter>=2)  
 {  
 Box::stop("The same user can't log in twice.");  
 infolog.shutDown(true);  
 }  
 }  

As I am working for case

We need code to allow open only one instace per user at a time except admin login.

I  implemented code in application class its working fine but problem is

if admin login then he can open multiple instance and other user which are not admin but admin
group added then they can not open multiple instance that right and its requirement.

but if admin group is not added to the user then they also able to open multiple instance that  I
need to restrict to open multiple instance.

problem is if admin group is not added to user then application class does not execute so code effect
not coming.

so I want any class name which execute at startup of instance for all user.