TNS-12535: TNS:operation timed out

Specific to Oracle 11G

If you see the errors in the alert logfile :

*********************************************************************** 

Fatal NI connect error 12170. 

  VERSION INFORMATION: 
        TNS for Linux: Version 11.2.0.2.0 - Production 
        Oracle Bequeath NT Protocol Adapter for Linux: Version 11.2.0.2.0 - Production 
        TCP/IP NT Protocol Adapter for Linux: Version 11.2.0.2.0 - Production 
  Time: 11-DEC-2011 15:08:18 
  Tracing not turned on. 
  Tns error struct: 
    ns main err code: 12535 

TNS-12535: TNS:operation timed out 
    ns secondary err code: 12560 
    nt main err code: 505 

TNS-00505: Operation timed out 
    nt secondary err code: 110 
    nt OS err code: 0

It may be due to the usage of Oracle Grid Control. To fix the issue you have to add the 2 lines below in your sqlnet.ora

SQLNET.ENCRYPTION_TYPES_SERVER=(3DES168)
SQLNET.ENCRYPTION_SERVER=REQUIRED