document.forms.agreement.agreecheck is null or not an object

[toniya]

1) Script Title: "Accept terms" form submission

2) Script URL (on DD): http://www.dynamicdrive.com/dynamici...acceptterm.htm

3) Describe problem: document.forms.agreement.agreecheck is null or not an object

I am getting above error on my pages; e.g. http://www.1websiteshostingpromotions.com/platinum.php

How to fix it?
Thanks and regards,
Toniya

p.s We changed the form names and agree names (we have 3 forms on same page) and look like it is fixed

Great Script; but needs another feature also - it is switching on 'submit' when box is ckecked but it should switch off 'submit' once it is pressed to avoid duplication.