TNS-12516 TNS:listener could not find instance with matching protocol stack

Few days ago I encountered an unfamiliar error to me, I wanted to connect to the database but I got stuck with TNS-12516 TNS:listener could not find instance with matching protocol stack

Basically what it means is that the listener “thinks” that there are no more available processes (you have reached maximum load) on the instance and it cannot create new connections.
Solution to this is modifying/increasing the PROCESSES init parameter (http://docs.oracle.com/cd/E11882_01/server.112/e10595/create005.htm#i1014287)
For more details you can check Oracle Support Note 240710.1

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