System.Web.HttpException: Request timed out error?

I have a thread class which makes a web request. After 20-30 urls request, its开发者_运维百科 throwing exception: System.Web.HttpException: Request timed out. My code is below where it is throwing exception:

httpReq.AllowAutoRedirect = false;
        httpReq.KeepAlive = false;
        httpReq.Headers.Add("Location", "");
        httpReq.Timeout = this.HttpRequestTimeout;

        httpRes = (HttpWebResponse)httpReq.GetResponse();

In last line : httpRes = (HttpWebResponse)httpReq.GetResponse(); it is throwing exception. "The remote server returned an error: (403) Forbidden."

I am using session for setting some values with the request header.

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I got the answer. I was not using httpRes.close() method after using response object. That's why after 80-90 request it was returning : "The remote server returned an error: (403) Forbidden ".