Can't figure out exception message

I am having the following error message and I am using petaPOCO. Why am I having this error message and What am I doing wrong to have this message:

{"There is already an open DataReader associated with this Command which must be closed first."}

This is what I have been able to copy for the exception message.

System.InvalidOperationException was caught Message=There is already an open DataReader associated with this Command which must be closed first. Source=System.Data StackTrace: at System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command) at System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command) at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) at System.Data.SqlClient.SqlCommand.ExecuteScalar() at PetaPoco.Database.Insert(String tableName, String primaryKeyName, Boolean autoIncrement, Object poco) in C:\Dev\Code\API\Models\PetaPoco.cs:line 1243 InnerException:

Solution

Here is an excellent explanation why this exception is raised:

http://blogs.msdn.com/b/spike/archive/2009/08/20/there-is-already-an-open-datareader-associated-with-this-command-which-must-be-closed-first-explained.aspx

The conclusion is as following:

Because the SqlDataReader keeps the memory stream (resultset) available until you explicitly close the SqlDataReader you can get this exception if you try to create a new reader without closing the previous one.

Alter your code to have a using statement whenever you create a SqlDataReader:

SqlCommand cmd = new SqlCommand(sql, con);
using (SqlDataReader rdr = cmd.ExecuteReader())
{
  while (rdr.Read())
  {
    Console.WriteLine("cid: {0}, ctext: {1}", rdr[0].ToString(), rdr[1].ToString());
  }
}

Using will automatically call dispose() (which closes the reader) when the closure (ending } ) is reached.

If this exception is raised in petaPOCO then there is a bug in their code or you are using the code in an unspecified way.