No data in Design Preview

[Jorge]

If the table adapter in dataset use connection string stored in Web.config, the report works OK when running the web page but show no data while previewing in Design mode.

I tried the solution proposed in forums but didn't work.

            ConnectionStringSettings connSettings = ConfigurationManager.ConnectionStrings["myConnectionString"];
            if ((connSettings != null) && (connSettings.ConnectionString != null))
            {
                this.hospitalDataSetTableAdapter1.Connection.ConnectionString = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
            }

I debug Design Preview with a MessageBox like this...

            }
            catch (System.Exception ex)
            {
                // An error has occurred while filling the data set. Please check the exception for more information.
                MessageBox.Show(ex.Message);
                System.Diagnostics.Debug.WriteLine(ex.Message);
            }

and I get "Object not set to an instance of an object"

What am I missing?
Thanks a lot!

[Jorge]

I traced the exception and It's generated inside InitConnection() in table adapter.

     private void InitConnection() {
            this._connection = new global::System.Data.SqlClient.SqlConnection();
            this._connection.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
        }

Somehow System.Configuration.ConfigurationManager.ConnectionStrings["myConnectionString"] it's not initializing correctly.
Again: This only happens in Design Time.

More ideas?