SSIS HTTP Connection and Script Task to consume RESTful Services API

I am trying to connect to a RESTful API using SSIS.  I have an HTTP Connection Manager with the URL and the username and password to gain access to the API.  The problem comes when I am trying to insert variables into the URL to determine the date range.  I am using a Task Script component to try to by pass the url in the Connection Manager and insert the variables into the URL.  I am attaching the code I am using and the error I get.  The error only comes when I try to run the SSIS package.  

public void Main()
		{
            // Get the unmanaged connection object, from the connection manager called "HTTP Connection Manager"
            object nativeObject = Dts.Connections["HTTP Connection Manager"].ConnectionString = ("https://api.apisource.com:8182/api/fleets/young/platforms/311305/data?descriptions=true&values=true&parameterId=10245&startTime=" + ((DateTime)Dts.Variables["startTime"].Value) + "&endTime=2015-09-09&maxCount=1000&startPort=-1&resolution=all");

            // Create a new HTTP client connection
            HttpClientConnection connection = new HttpClientConnection(nativeObject);

            // Download the file #1
            // Save the file from the connection manager to the local path specified
            string filename = "C:\\Temp\\Sample.txt";
            connection.DownloadFile(filename, true);

            // Confirm file is there
            if (File.Exists(filename))
            {
                MessageBox.Show(string.Format("File {0} has been downloaded.", filename));
            }


            // Download the file #2
            // Read the text file straight into memory
            byte[] buffer = connection.DownloadData();
            string data = Encoding.ASCII.GetString(buffer);

            // Display the file contents
            MessageBox.Show(data);


			
			Dts.TaskResult = (int)ScriptResults.Success;
		}
		}

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