ORA-12516, TNS:listener could not find available handler with matching protocol stack

My charbench client was running fine with 100 users against an Oracle 11g R2 database created using swingbench, but when I tried to run the client with 200 users I got the following error message:

Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error: ORA-12516, TNS:listener could not find available handler with matching protocol stack

On checking to see the vaule of the process for the database I noticed that it was set to 150.

SQL> show parameter processes; NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ aq_tm_processes integer 0 db_writer_processes integer 1 gcs_server_processes integer 0 global_txn_processes integer 1 job_queue_processes integer 1000 log_archive_max_processes integer 4 processes integer 150 SQL> show parameter spfile; NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ spfile string +DATA/testasm/spfiletestasm.or a SQL> alter system set PROCESSES=250 scope=spfile; System altered. SQL> shutdown immediate; Database closed. Database dismounted. ORACLE instance shut down. SQL> startup; ORACLE instance started. Total System Global Area 3540881408 bytes Fixed Size 2211864 bytes Variable Size 1644171240 bytes Database Buffers 1879048192 bytes Redo Buffers 15450112 bytes Database mounted. Database opened. SQL> show parameter processes; NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ aq_tm_processes integer 0 db_writer_processes integer 1 gcs_server_processes integer 0 global_txn_processes integer 1 job_queue_processes integer 1000 log_archive_max_processes integer 4 processes integer 250 SQL>

The charbench client proceeded file with 200 users after the above change to the PROCESSES parameter.