Format of the initialization string does not conform to specification starting at index 0.

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C#

Hi..

I am working on WebApplication.In that I have created a method in datalayer by taking Datatable.For Datatable I have written the following code in SqlHelper.cs,

public static DataTable ExecuteDataTable(string storedProcedureName,params SqlParameter[] arrParam)
  {
    DataTable dt = new DataTable();

    // Open the connection
    using (SqlConnection cnn = new SqlConnection("connectionString"))
    {
        cnn.Open();

        // Define the command
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.Connection = cnn;
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.CommandText = storedProcedureName;

            // Handle the parameters
            if (arrParam != null)
            {
                foreach (SqlParameter param in arrParam)
                    cmd.Parameters.Add(param);
            }

            // Define the data adapter and fill the dataset
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                da.Fill(dt);
            }
        }
    }
    return dt;
  }

So when i am running this its shows the runtime error "Format of the initialization string does not conform to specification starting at index 0."
and
"using (SqlConnection cnn = new SqlConnection("connectionString"))"

I donot understand how to solve this..Anybody is there please help me.

Thanks..