The remote server returned an error: (403) Forbidden

Question

I\'ve written an app that has worked fine for months, in the last few days I\'ve been getting the error below on the installed version only.

If I run the source code

Answer 1

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]";