Error when try to download the manifest file

[Josjos23]

When I try to download the manifesft file from the playbackUrl, http://...ism/manifest(format... always return " The remote server returned an error: (403) Forbidden."

43 var httpRequest = (HttpWebRequest)WebRequest.Create(new Uri(playbackUrl));
44 httpRequest.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);
45 httpRequest.Timeout = 30000;
46 var httpResponse = httpRequest.GetResponse();

But if I put the playbackUrl into the web explorer I can download the manifest file without problems...

any idea?

thanks.