可能是你关闭了与此transaction关联的connection,一般使用的结构如下:
using (SqlConnection connection = new SqlConnection(@"..."))
{
       using (SqlTransaction trans = connection.BeginTransaction())
       {
            try
            {
                    trans.Commit();
            }
            catch
            {
                    trans.Rollback();
            }
        }
}