Log In User element error

I wanted to add a members' area on a website that I run, so I did the usual insert log in user. When I did so, I got the following error boxes:

While executing canApplyServerBehavior in Login User.htm, a JavaScript error occured.

While executing onLoad in Login User.htm, the following JavaScript error(s) occured:

At line 875 of file "C:\Program Files (x86)\Adobe\Adobe DreamweaverCS5\Configuration\ServerBehaviors\PHP_MySQL\Login User.js": tagList.getAttribute("NAME") has no properties

Any ideas or solutions?

Thanks!