Add the following line:
request.UseDefaultCredentials = true;
This will let the application use the credentials of the logged in user to access the site. If it’s returning 403, clearly it’s expecting authentication.
It’s also possible that you (now?) have an authenticating proxy in between you and the remote site. In which case, try:
request.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
Hope this helps.
Looks like problem is based on a server side.
Im my case I worked with paypal server and neither of suggested answers helped, but http://forums.iis.net/t/1217360.aspx?HTTP+403+Forbidden+error
I was facing this issue and just got the reply from Paypal technical.
Add this will fix the 403 issue.
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.UserAgent = “[any words that is more than 5 characters]”;