When you use ODAC to link an Oracle database, Conn. Open () Error: an instance of the object is not set to an object reference. Oracle.DataAccess.dll version: 4.121.2.0 ODAC release 4OracleClient version: Oracle 12c Release 4 scenario one (verified feasible): (1) Server installation 32-bit ODAC with Oracle Developer Tools for Visual Studio downloads,:http://www.oracle.com/technetwork/topics/dotnet/ Utilsoft-086879.html. (2) Download the ODAC XCopy version,:http://www.oracle.com/technetwork/database/windows/downloads/ Utilsoft-087491.html (3) Unzip ODAC XCopy version and locate the Instantclient_12_1 folder. (4) Copy the files in the Instantclient_12_1 folder to the Bin folder of the Oracle 12c RELEASE4 installation directory, if there are duplicate files skipped. Scenario two (not verified): Replace the Oracle.DataAccess.dll reference in the project with the Oracle.ManagedDataAccess.dll. Modify Providername= "Oracle.ManagedDataAccess.Client" in connnectionstring.
Oracle.DataAccess.Client.OracleConnection.Open () error system. NullReferenceException