System.Runtime.InteropServices.ExternalException on calling Oracle.DataAccess.Client.OracleConnection.Open()

Question

I have following code to connect to a database using ODP.net:

// connection information removed to protect sensitive information
string host = "******";
string sid = "*****";
string connectDescriptor = string.Format("(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST={0})(PORT=1521))(CONNECT_DATA=(SID={1})))", host, sid);
string username = "*****";
string password = "*****";

string connectionString = string.Format("Data Source={0};User ID={1};Password={2};", connectDescriptor, username, password);
OracleConnection conn = null;

try
{
    conn = new OracleConnection(connectionString);
    conn.Open();
}
catch (OracleException oraex)
{
    MessageBox.Show(oraex.ErrorCode + ": " + oraex.Message);
}
finally
{
    conn.Close();
}

Call to Open() throws an error, and I am unable to figure out much about it. oraex.ErrorCode is -2147467259 and oraex.Message is "". Trying to access most members of the thrown exception results in a NullReferenceException.

Also, I can see that the base exception is a System.Runtime.InteropServices.ExternalException.

What is going on here? Because of the InteropServices exception I am guessing that it is something to do with COM.

Extra information

• I have just installed ODAC 12c.
• Connection information is verified. I can connect to same database using a SilverLight application which uses deprecated System.Data.OracleClient. They are OK.

Answer 1

Sounds like it's something with the oracle client. I've faced similar issues with web projects while the console projects were working just fine. If you installed 64bit ODAC, then uninstall it completely and try with 32bit. Also double check the target platform at Visual Studio is "32bit". If that works, you can search what was wrong with 64 bit installation.