Fatal NI connect error 12502

When logging to the database during peak hours, the following error is thrown intermittently: ORA-12502 TNS:listener received no CONNECT_DATA from client. A temporary workaround would be to restart the listener.

Fatal NI connect error 12502, connecting to:

(DESCRIPTION=(LOAD_BALANCE=yes)(ADDRESS=(PROTOCOL=TCP)(HOST=10.1.25.12)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=a012band)(CID=(PROGRAM=sqlplus@narayan)(HOST=narayan)(USER=fnsonla))))

VERSION INFORMATION:
TNS for IBM/AIX RISC System/6000: Version 9.2.0.7.0 - Production
TCP/IP NT Protocol Adapter for IBM/AIX RISC System/6000: Version 9.2.0.7.0 - Production
Time: 12-DEC-2007 11:36:13
Tracing not turned on.
Tns error struct:

Client trace could also show ORA-12520: TNS:listener could not find available handler for requested type of server

An increase in the number of connections can cause this problem to manifest where it did not exist earlier.
Check if the processes parameter has exhausted using following command by log in into database as SYSDBA:

select * from v$resource_limit where resource_name='processes';

The pfile setting for PROCESSES is not adequate for customer setup. When the database process limit is hit, the listener will not be able to spawn any more server processes. Hence connections are failing with ORA-12502 at client side as well as in the listener trace and listener.log files
Solution
Increase the value for PROCESSES for all instances in the RAC cluster.