Throw error to presentation

Hi,
From presentation layer, I am calling a method in DAL to execute a stored procedure in the database. When executing the stored procedure it caused an error. What I am trying to do is to pass this error via using throw so in the presentation layer I catch the throw and show a user a dialog box to read the error message.
My question is how can I pass the   msg  variable in t he alert() method. I know if I make it static it works, but what I need to do is to make the message dynamic by reading it from the ex.Message.
The error I am getting is that >>> Error: 'msg' is undefined.... but I already declared the msg variable  as shown in block catch below.... please advise ... Bob
in DAL method...
            catch (System.Data.SqlClient.SqlException exc)
            {
     &n ...