ORA-06502: PL/SQL: numeric or value error: character to number conversion error ORA-06512: at line 1

Hi,

I am calling an Oracle stored procedure from an ASP.Net application.

The Oracle Stored Procedure is:

----------------------------------------------------------------------
CREATE OR REPLACE PROCEDURE simple_test (

   a_UserCode      IN varchar2,

   a_ErrorMsg      OUT varchar2) AUTHID CURRENT_USER

AS

BEGIN

 a_ErrorMsg  := a_UserCode || 'test' ;

END;
----------------------------------------------------------------------

This procedeure works fine when I run it in SQL Plus, but when I run it from ASP.Net I get the following error:

----------------------------------------------------------------------
ORA-06502: PL/SQL: numeric or value error: character to number conversion error ORA-06512: at line 1
----------------------------------------------------------------------

The ASP.Net code is :

----------------------------------------------------------------------
        OleDbConnection1.Open()

        OleDbCommand1.CommandText = "simple_test"
        OleDbCommand1.CommandType = CommandType.StoredProcedure

        OleDbCommand1.Parameters.Add("a_UserCode", OracleType.VarChar)
        OleDbCommand1.Parameters("a_UserCode").Value = "TEST"

        OleDbCommand1.Parameters.Add("a_ErrorMsg", OracleType.VarChar)
        OleDbCommand1.Parameters("a_ErrorMsg").Direction = ParameterDirection.Output

        OleDbCommand1.ExecuteNonQuery()

        Label1.Text = OleDbCommand1.Parameters("a_ErrorMsg").Value

        OleDbConnection1.Close()
----------------------------------------------------------------------

Appreciate if anyone can help. I suspect the "OracleType.VarChar" as it should be VarChar2, but this is not availabe in ASP.Net and also you can't set the size of it from ASP.Net!