WWW class is empty on iOS

I have some networking code using Unity's WWW class that reads data from a remote server. It works fine in the editor, but when I try it from an iPad the www object is completely empty - no headers, no error, nothing. Here's a stripped down version of what I'm doing: WWW www; public void StartLogin (string username, string password) { WWWForm form = new WWWForm(); form.AddField("username", username); Hashtable headers = form.headers; headers["username"] = username; headers["password"] = password; headers["deviceId"] = 2; www = new WWW(loginUrl, form.data, headers); //StartCoroutine(WaitForLoginRequest()); } void Update() { if (www != null && www.isDone) { DoLoginRequest(); } } void DoLoginRequest() { //Code goes here www = null; } As you can see, I started using coroutines, but switched over to a simpler version using Update (didn't help). I know the connection is getting through to the server because it's logging an error 412 - I can fix that, but I'm more worried about where all my information is going on the iOS side.