If you are running Application Server 8.1 on Red Hat Linux, the stack size of the threads created by the Red Hat OS for Application Server is 10 Mbytes, which can cause JVM resource problems when the number of Access Manager user sessions reaches 200.
Workaround: Set the Red Hat OS operating stack size to a lesser value such as 2048 or even 256 Kbytes, by executing the ulimit command before you start Application Server. Execute the ulimit command on the same console that you will use to start Application Server. For example:
# ulimit -s 256;