.net entity framework with oracle 11g

It looks like the managed driver is unable to resolve TNS names.You should make sure your configuration is correct (see Documentation).

For example:

<oracle.manageddataaccess.client>  ...  <settings>    ...    <setting name="TNS_ADMIN" value="C:\path\where\TNSNAMESFILE\is"/>    ...  </settings>  ...</oracle.manageddataaccess.client>

Also, you may need to configure the provider factory if not already defined in machine.config:

<system.data>  <DbProviderFactories>    <remove invariant="Oracle.ManagedDataAccess.Client" />    <add name="ODP.NET, Managed Driver"      invariant="Oracle.ManagedDataAccess.Client"      description="Oracle Data Provider for .NET, Managed Driver"      type="Oracle.ManagedDataAccess.Client.OracleClientFactory, Oracle.ManagedDataAccess, Version=4.121.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342" />  </DbProviderFactories></system.data>

As an aside, I noted you are mentioning Oracle.ManagedDataAccessDTC as the managed driver. Please note that Oracle.ManagedDataAccessDTC is actually the component that provides support for distributed transactions, while the main driver assembly is called "Oracle.ManagedDataAccess".