title: Connecting to Oracle DB from IIS. Error: The underlying provider failed on Open
body: <p>I get the following error when attempting to consume a WCF Service hosted in IIS 8.5. <code>The underlying provider failed on Open.</code> I am using an <code>Oracle DB 11G</code>.</p>
  
  <p>From my development environment, I am able to connect to <code>Oracle DB</code> with no issues. If I simply Run the WCF Service within Visual Studio and run the Client Application. I am also able to Connect to the Oracle Instance from within <code>Visual Studio</code> and consume the service.</p>
  
  <p>I am not sure where to look. Finally, I turned off Firewall on the Development Server just to see if there was any issues. I am also able to Ping the Oracle Server with success.</p>
  
  <p>Here is the Connection String from IIS:</p>
  
  <pre><code>metadata=res://*/OracleDB.csdl|res://*/OracleDB.ssdl|res://*/OracleDB.msl;provider=Oracle.ManagedDataAccess.Client;
  provider connection string="DATA SOURCE=INSTANCE_TNSNAMES;PASSWORD=MyPassword;
  PERSIST SECURITY INFO=True;USER ID=MyUserID"
  </code></pre>
  
  <p>This is the connection string added to the application via Nuget when Oracle Managed Drivers are installed in Visual Studio and it is the same string in the application.</p>
  
  <p>Update: Here is a list of things I tried:</p>
  
  <p>Things I have tried:</p>
  
  <ol>
  <li>Installed Oracle Instant Client on the Windows Server running IIS</li>
  <li>Create TNS_ADMIN variable in Environment Variable</li>
  <li>Set Path to Oracle Instant Client</li>
  <li>Add (install) ODBC drivers to the instant client folder</li>
  <li>Create and configured tnsnames.ora</li>
  </ol>
  
  <p>Still getting the same error:</p>