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

I got this error while trying to connect to a database from one of our new application servers.

oerr returned the following:

$ oerr ora 12516
12516, 00000, "TNS:listener could not find available handler with matching protocol stack"
// *Cause: None of the known and available service handlers for the given
// SERVICE_NAME support the client's protocol stack: transport, session,
// and presentation protocols.
// *Action: Check to make sure that the service handlers (e.g. dispatchers)
// for the given SERVICE_NAME are registered with the listener, are accepting
// connections, and that they are properly configured to support the desired
// protocols.


This message did not help as I had ensured that the tnames.ora is properly configured and I was sure of the SERVICE name.

SOLUTION:

 I increased processes parameter to 3000.

alter system set processes=3000 scope=spfile;

The database was restarted. Then the error below showed up!

ORA-00371: not enough shared pool memory, should be atleast 5207647846 bytes

This was fixed by modifying the shared_pool_memory parameter to a little over the suggested value above.

Issued solved!