Hi all,
 we are developing a big application on J2ee. The size of ear is nearly say 20 MB.
  The Problem is some times when 20 concurrent users are accessing the application , then my server is hanging Up.
But when we tested with the testing tools even it is fine for 500 users.

Pls let me the reasons for this cause.
Is it application server problem or OS problem or any other problem.
we are using linux 7.2 as OS
Its very argent