ODP.NET Oracle.ManagedDataAccess causes ORA-12537 network session end of file

Edit: ASO is now supported. Upgrade to ODAC 12c Release 4 or later. If this does not fix your problem, check the alert.log on the database server and investigate (google) any errors that occur there when you attempt to connect.

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Original Answer:

As of this writing (4/30/15) there is no support for Oracle Advanced Security Option (ASO) encryption with ODP.NET Managed Driver which is what is causing your errors.

This is very likely to be supported at some point in the future so if you are reading this at a later date, check the latest ODP.NET docs to see if an upgrade of ODP.NET is needed.

http://docs.oracle.com/cd/E56485_01/win.121/e55744/InstallConfig.htm#CHDJIDIG

As of October 5th, 2015, the Oracle.ManagedDataAccess driver (ODAC 12c Release 4) supports ASO.

https://apex.oracle.com/pls/apex/f?p=18357:39:18138408495219::NO::P39_ID:28201