Quick resolution: Give full permission to AUTHENTICATED USERS in following folders. a) ORACLE_HOME b) Program Files\ORACLE   Check your PATH. You might have installed different clients in your system and your .NET application is pointing to a home with inappoperiate client. What your .NET application should load is OCI.DLL with File version more than 8.1.7. According to the MSDN document Oracle and ADO.NET:   "The .NET Framework Data Provider for Oracle provides access to an Oracle database using the Oracle Call Interface (OCI) as provided by Oracle Client software. The functionality of the data provider is designed to be similar to that of the .NET Framework data providers for SQL Server, OLE DB, and ODBC. "     The MSDN document System Requirements (Oracle) says: "The .NET Framework Data Provider for Oracle requires Microsoft Data Access Components (MDAC) version 2.6 or later. MDAC 2.8 SP1 is recommended. You must also have Oracle 8i Release 3 (8.1.7) Client or later installed. "   Both the .NET Framework Data Provider for Oracle and Oracle Data Provider for .NET are data providers to access Oracle database. The former ships with .NET Framework and requires Oracle client version 8.1.7 or above. The latter is provided by Oracle company and requires Oracle client version 9.2 or later.     The Oracle Data Provider for .NET (ODP.NET) features optimized ADO.NET data access to the Oracle database. ODP.NET allows developers to take advantage of advanced Oracle database functionality, including Real Application Clusters, XML DB, and advanced security.   See the document Comparing the Microsoft .NET Framework 1.1 Data Provider for Oracle and the Oracle Data Provider for .NET for more information about the difference.