cannot run more than 6 jvms on one machine

[stanley.shi]

Hi guys, I have a very strange problem here, hope someone can help.

I have a virtual machine with 8 GB memory, the os is CentOS 5.5 x64 version; I 
got this VM from someone else (means they may have done some configuration on 
this VM)
I cannot start even 6 easiest jvm at the same time (for example, start the 
following java code simultaneously 6 times:

import java.io.IOException;
public class InputTest {
        public static void main(String[] args) throws IOException, 
InterruptedException {
                int length = 0;
                long sum=0;
                do {
                        sum+=length++;
                        System.out.println("Current sum: "+ sum);
                        Thread.sleep(1000);

                } while (length <1000000);

        }
}


Any one  have any comments?

Thanks,
Stanley