The problem is known to occur when Access Manager 7.0 is deployed a web server, and the "-Xss128k" JVM option is used with 64-bit JVM on the web container. The problem can occur with any java application. For 64-bit JVM's, the minimum per thread stack size should be 256k, -Xss256k, or even 512k since 64-bit VM's default per thread stack size is 1 mb.
Solution: For 64-bit JVMs, the minimum per thread stack size should be 512k since the 64-bit JVM default per thread stack size is 1 mb. The 64-bit JVM support was introduced starting with Web Server 6.1 SP5. Application Server 8.1 and 8.2 do not support 64-bit JVM, but Application Server 9.1 will. Access Manager and its amtune scripts support 64-bit JVM starting with AM 7.0 Patch 5. For more information, see http://java.sun.com/docs/hotspot/threads/threads.html