Server Error in '/behtop website' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.  Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Source Error:

Line 124:        SqlCommand cmd = new SqlCommand("ViewEstate1", _cn);
Line 125:        cmd.CommandType = CommandType.StoredProcedure;
Line 126: cmd.Parameters.AddWithValue("@Type", ddltype.SelectedItem.Text); Line 127:        cmd.Parameters.AddWithValue("@Transfer", ddlTran.SelectedItem.Text.Trim());
Line 128:        cmd.Parameters.AddWithValue("@measure", ddlmeter.SelectedItem.Text.Trim());