SSL Problem: Trust Security Relationship Issue

Is there a  solution that could not be potential security threat if I turn off the SSL certificate validation. This is production code, I understand that there will be the risk of the server that I will be connecting to in this case. We are currently migrating our C# biased hotel management system program toasp.net to adopt and compete to web applications for hotels. This will be an a live application with a domain. I am worried with the SSL security threat while authentication. Can anyone share a better secure code resolutions for my code below?

Thank you.

 Error: C# The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel

public string SendRequest(string url, string postData) {
		var uri = new Uri(url);
		var request = WebRequest.Create(uri);
		var encoding = new UTF8Encoding();
		var requestData = encoding.GetBytes(postData);

		request.ContentType = "application/x-www-form-urlencoded";
		request.Method = "POST";
		request.Timeout = (300*1000); //TODO: Move timeout to config
		request.ContentLength = requestData.Length;		

		using (var stream = request.GetRequestStream()) {
		stream.Write(requestData, 0, requestData.Length);
		}

		var response = request.GetResponse();

		string result;

		using (var reader = new StreamReader(response.GetResponseStream(), Encoding.ASCII)) {
		result = reader.ReadToEnd();
		}

		return result;
}