URL Unauthorized access error while accessing files from dropbox?

Here the code is .

public string GenerateSignature(Uri url, string consumerKey, string consumerSecret, string token, string tokenSecret, string httpMethod, string timeStamp, string nonce, SignatureTypes signatureType, out string normalizedUrl, out string normalizedRequestParameters)
    {
        normalizedUrl = null;
        normalizedRequestParameters = null;
        string signatureBase = string.Empty;
        string secretBase = string.Empty;
        switch (signatureType)
        {
            case SignatureTypes.PLAINTEXT:
                return UrlEncode(string.Format("{0}&{1}", consumerSecret, tokenSecret));
            //signatureBase = GenerateSignatureBase(url, consumerKey, token, tokenSecret, httpMethod, timeStamp, nonce, HMACSHA1SignatureType, out normalizedUrl, out normalizedRequestParameters);
            case SignatureTypes.HMACSHA1:
                signatureBase = GenerateSignatureBase(url, consumerKey, token, tokenSecret, httpMethod, timeStamp, nonce, HMACSHA1SignatureType, out normalizedUrl, out normalizedRequestParameters);
                secretBase = string.Format("{0}&{1}", UrlEncode(consumerSecret), string.IsNullOrEmpty(tokenSecret) ? " : UrlEncode(tokenSecret));
                var crypt = MacAlgorithmProvider.OpenAlgorithm(MacAlgorithmNames.HmacSha1);
                var buffer = CryptographicBuffer.ConvertStringToBinary(signatureBase, BinaryStringEncoding.Utf8);
                var keyBuffer = CryptographicBuffer.ConvertStringToBinary(secretBase, BinaryStringEncoding.Utf8);
                var key = crypt.CreateKey(keyBuffer); var sigBuffer = CryptographicEngine.Sign(key, buffer);
                return CryptographicBuffer.EncodeToBase64String(sigBuffer);
            case SignatureTypes.RSASHA1:
                throw new NotImplementedException();
            default:
                throw new ArgumentException("Unknown signature type", "signatureType");
        }
    }