To find the root cause of this, need to investigate arjavaplugin log file in AR_HOME/DB folder
If not root cause found from the log, change the log level to Trace as below.
To change the log level got to AR System Administrator console->General -Plugin Server Configuration
Select the plugin server instance identified by port - Port 9999 - AR Plugin server
Change the log level to Trace and restart AR server.
Check the arjavaplugin log file.