'ClsDatabase.GetDS(string, string, System.Data.DataSet, System.Data.SqlClient.SqlCommand)': not all code paths return a value error in C#

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.NET3.5

C#

.NET

In my class file i have following code:

public Double GetScalarRes(String CmdStr, SqlCommand SqlCmd, String strConArc)
    {
        // This function return only 1 value i.e. double value.
        // It takes Query String and execute it on SQL server and returns only one value.

        double Res = 0;


        try
        {
            // checking whether connection string from web.config file is "strConString".
            // accordingly setting the connection object.

            if (strConArc == "strConString1")
            {
                con = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["strConString1"]);
            }
            else
            {
                con = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["strConString"]);
            }
            con.Open();

            if ((SqlCmd != null))
            {
                SqlCmd.Connection = con;

                // returns only 1 value.
                //Res = Convert.ToDouble(SqlCmd.ExecuteScalar);
                Res = Convert.ToDouble(SqlCmd.ExecuteScalar());
            }
            else
            {
                SqlCommand Cmd = new SqlCommand(CmdStr, con);

                // returns only 1 value.
                //Res = Convert.ToDouble(Cmd.ExecuteScalar);
                Res = Convert.ToDouble(SqlCmd.ExecuteScalar());
            }

            // close connection.
            con.Close();

            // return double value.
            return Res;

        }
        catch (Exception ex) { }

    }

Syntax is correct but while compileing in enviroment it gives me error
like

ClsDatabase.GetDS(string, string, System.Data.DataSet, System.Data.SqlClient.SqlCommand)': not all code paths return a value

But in VB.NET it works perfect. Am biginner of C#.

Can somebody Help me to resolve the issue.

Thanks in Advance
Yogesh