use 'Java Vuser' protocol in LoadRunner meet error "Cannot start replay due to compilation error"

Hello,

When I use 'Java Vuser' protocol in LoadRunner 12 meet error "Cannot start replay due to compilation error".

I also set the CLASSPATH env variables.

and the code in Actions as belows:(Sample)

/*
 * LoadRunner Java script. (Build: _build_number_)
 * 
 * Script Description: 
 *                     
 */
import com.*;

 

import lrapi.lr;

public class Actions
{
	
	
	
	
	public int init() throws Throwable {
		
		
		return 0;
	}//end of init


	public int action() throws Throwable {
		
		Demo100.main((String[])null);
		return 0;
	}//end of action


	public int end() throws Throwable {
		return 0;
	}//end of end
}

 Could anybody give me some suggestions?

thanks.