C# 调C++ dll文件.报:无法加载XXX.dll,找不到指定模块解决办法

        [DllImport("EncrySign.dll", EntryPoint = "GenSimpleKey")]
        public static extern string GenSimpleKey(int dwLen);

        private void button1_Click(object sender, EventArgs e)
        {
            string s =GenSimpleKey(10);
            MessageBox.Show(s);
        }