Error On returning Boolean - Stored Procedure (Oracle)

Hi,
When I try to return a boolean value from a stored funciton in oracle. I get an error. How should i Specify the returnvalue parameter if the parameter is boolean.

Dim ReturnValue As OleDb.OleDbParameter = Selectcmd.Parameters.Add("ReturnValue", OleDb.OleDbType.Boolean)
ReturnValue.Direction = ParameterDirection.ReturnValue

What is wrong with the above code?. I even tried specifying a length
Dim ReturnValue As OleDb.OleDbParameter = Selectcmd.Parameters.Add("ReturnValue", OleDb.OleDbType.Boolean,10)
It does not work either. If I use any other type as the return type of the function it works fine. Any Pointers would be appreciated.

Error:
System.Data.OleDb.OleDbException:  at System.Data.OleDb.OleDbCommand.ExecuteCommandTextErrorHandling(Int32 hr) at System.Data.OleDb.OleDbCommand.ExecuteCommandTextForMultpleResults(tagDBPARAMS dbParams, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommandText(Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommand(CommandBehavior behavior, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior behavior, String method) at System.Data.OleDb.OleDbCommand.ExecuteNonQuery() at WebApplication2.WebForm1.DEDR_Update(Object Sender, DataGridCommandEventArgs E) in C:\Inetpub\wwwroot\c$\inetpub\wwwroot\WebApplication2\WebForm1.aspx.vb:line 470

Code:
Dim selectCmd As New OleDb.OleDbCommand("test2", myConnection)

selectCmd.CommandType = CommandType.StoredProcedure

Dim ReturnValue As OleDb.OleDbParameter = Selectcmd.Parameters.Add("ReturnValue", OleDb.OleDbType.Boolean)

ReturnValue.Direction = ParameterDirection.ReturnValue

'Input Values

selectCmd.Parameters.Add(New OleDb.OleDbParameter("@customer_no_", OleDb.OleDbType.VarChar, 255))

selectCmd.Parameters("@customer_no_").Direction = ParameterDirection.Input

selectCmd.Parameters.Add(New OleDb.OleDbParameter("@credit_card_id_", OleDb.OleDbType.Integer))

selectCmd.Parameters("@credit_card_id_").Direction = ParameterDirection.Input

'Assign Values

selectCmd.Parameters("@customer_no_").Value = "1000"

selectCmd.Parameters("@credit_card_id_").Value = 1

'Execute the function

selectCmd.ExecuteNonQuery()

Dim a As String = selectCmd.Parameters("ReturnValue").Value

Response.Write("Value" + a)