Hi Alan,
So what are the actual symptoms? I've pasted your code into a new page here, changed the website ID, password and checklist ID to something on my database and it works fine so at least there is nothing wrong in your code.
For now I will assume the problem is that the control appears but if you type in something it does not drop down with a list of species name matches? If so, here are a couple of things you can try:
1) If you use FireFox, try the Firebug addin. This lets you see AJAX calls on the Console tab, so you can check the response. E.g. if you have an incorrect website ID or password, you will get {"error":"Unknown Exception: unauthorised"} back, but the control will just appear to not work. In fact Firebug is an excellent tool for client-side web debugging so I'd recommend giving it a try if you haven't already.
2) Have you checked your application\logs folder to see if anything is posted when you try to use the control? As usual when debugging setting your log threshold to 4 in the config.php file will help capture the most information.
3) Try adding the following code to the page which will do a check of various settings and warn you of any problems:
echo data_entry_helper::system_check(true);
Let me know how you get on,
John van Breda
Biodiverse IT