程序在服务器上运行就会出错:系统找不到指定的文件,该如何解决

        //加密
        public static string Encode(string key)
        {
            dsa.FromXmlString(PRIVATE_KEY);
            System.Security.Cryptography.DSASignatureFormatter f = new System.Security.Cryptography.DSASignatureFormatter(dsa);
            f.SetHashAlgorithm("SHA1");
            Byte[] source = System.Text.ASCIIEncoding.ASCII.GetBytes(key);
            System.Security.Cryptography.SHA1Managed sha = new System.Security.Cryptography.SHA1Managed();
            Byte[] result = sha.ComputeHash(source);
            Byte[] regkey = f.CreateSignature(result);
            return Convert.ToBase64String(regkey);
        }