I'm using DataAssist to create my forms.
If you don't know about this type of thing - and why would you assume you were doing anything wrong when you're using an extension - then it won't work will it?
If you use the WebAssist > File Manipulation behaviour then you're doomed to it never working on an existing form. So what is the point of it?
Perhaps this is one for the feature request list.
Thanks for the advice