In AWS Load Balancing and Auto Scalling when the alarm fires and another instance launched .. my application crashes

I have a client-server application, I put the server module on EC2 instance and made a customized alarm with the auto scaling to launch new instance based on the number of users connected to the instance..

so if the number of clients using my server application reached 5, it launches another instance.. and it worked fine..

but after launching the new instance, all the client applications crashes.. any guess why is that?

note: I tested running many clients from private network.. that means all the clients requests will appear to the server coming from the same ip (don't know if that info. help)

Thanks in advance for your help