I am trying to see if a directory exists based on an input field from the user. When the user types in the path, I want to check if the path actually exists.

I have some c# code already. It returns 1 for any local path, but always returns 0 when I am checking a network path.

static string checkValidPath(string path)
{
    //Insert your code that runs under the security context of the authenticating user here.
    using (ImpersonateUser user = new ImpersonateUser(user, "", password))
    {
        //DirectoryInfo d = new DirectoryInfo(quotelessPath);
        bool doesExist = Directory.Exists(path);

        //if (d.Exists)
        if(doesExist)
        {
            user.Dispose();
            return "1";
        }
        else
        {
            user.Dispose();
            return "0";
        }
    }


}

public class ImpersonateUser : IDisposable
{
    [DllImport("advapi32.dll", SetLastError = true)]
    private static extern bool LogonUser(string lpszUsername, string lpszDomain, string lpszPassword, int dwLogonType, int dwLogonProvider, out IntPtr phToken);

    [DllImport("kernel32", SetLastError = true)]
    private static extern bool CloseHandle(IntPtr hObject);

    private IntPtr userHandle = IntPtr.Zero;
    private WindowsImpersonationContext impersonationContext;

    public ImpersonateUser(string user, string domain, string password)
    {
        if (!string.IsNullOrEmpty(user))
        {
            // Call LogonUser to get a token for the user
            bool loggedOn = LogonUser(user, domain, password,
                    9 /*(int)LogonType.LOGON32_LOGON_NEW_CREDENTIALS*/,
                    3 /*(int)LogonProvider.LOGON32_PROVIDER_WINNT50*/,
                    out userHandle);
            if (!loggedOn)
                throw new Win32Exception(Marshal.GetLastWin32Error());

            // Begin impersonating the user
            impersonationContext = WindowsIdentity.Impersonate(userHandle);
        }
    }

    public void Dispose()
    {
        if (userHandle != IntPtr.Zero)
            CloseHandle(userHandle);
        if (impersonationContext != null)
            impersonationContext.Undo();
    }
}

Any help is appreciated. Thanks!

EDIT 3: updated code to use BrokenGlass's impersonation functions. However, I need to initialize "password" to something...

EDIT 2: I updated the code to try and use impersonation as suggested below. It still fails everytime. I assume I am using impersonation improperly...

EDIT: As requested by ChrisF, here is the function that calls the checkValidPath function.

Frontend aspx file...

$.get('processor.ashx', { a: '7', path: x }, function(o) {
            alert(o);
            if (o=="0") {
                $("#outputPathDivValid").dialog({
                    title: 'Output Path is not valid! Please enter a path that exists!',
                    width: 500,
                    modal: true,
                    resizable: false,
                    buttons: {
                        'Close': function() { $(this).dialog('close'); }
                    }
                });
            }
        });

Backend ashx file...

public void ProcessRequest (HttpContext context) {
    context.Response.Cache.SetExpires(DateTime.Now);
    string sSid = context.Request["sid"];
    switch (context.Request["a"])
    {//a bunch of case statements here...
            case "7":
            context.Response.Write(checkValidPath(context.Request["path"].ToString()));
            break;