IE automation from a web service

Question

I have a unique problem where I need a copy of IE to do some session management and run some JavaScript on the page. The goal is to retrieve a value representing the server side session ID written by the JavaScript into the HTML response.

The code looks like this:

public class RemoteFileProcessor
{
    #region Fields (1) 

    private bool _navigating;

    #endregion Fields 

    #region Methods (2)

    public string GetSessionID(string URL)
    {
        string action = "";
        int count = 0;

        object nullObj = null;
        object url = URL;

        //Create an instance of IE
        SHDocVw.InternetExplorerClass ie = new SHDocVw.InternetExplorerClass();

        // Load the page from which to retrive the server side session identifier.
        _navigating = true;
        ie.DocumentComplete += ie_DocumentComplete;
        ie.Navigate2(ref url, ref nullObj, ref nullObj, ref nullObj, ref nullObj);

        // Wait while the page loads.
        while (_navigating && count <= 30)
        {
            System.Threading.Thread.Sleep(1000);

            count++;
        }

        // Get the form object from the page.
        mshtml.IHTMLDocument3 doc = (mshtml.IHTMLDocument3)ie.Document;
        mshtml.IHTMLElementCollection formElements = doc.getElementsByName("selectableHourlyLMPForm");
        System.Collections.IEnumerator enumerator = formElements.GetEnumerator();

        // Get the form action, which includes the JSessionID
        while (enumerator.MoveNext())
        {
            mshtml.IHTMLFormElement form = (mshtml.IHTMLFormElement)enumerator.Current;

            action = form.action;
        }

        ie.Quit();

        return action;
    }

    // Private Methods (1) 
    private void ie_DocumentComplete(object pDisp, ref object URL)
    {
        _navigating = false;
    }

    #endregion Methods 
}

When I run the above code in unit test on my XP machine it all works flawlessly.

When I run the code from a web service on our Win2k3 server from IIS under a service user, the internet explorer instance simply times out (takes 4-5 minutes) after the call to InternetExplorerClass.Navigate2().

Any solution would be welcome as I am at a complete loss for words on what is going on here...