Mhmm by experience I would say you have 1 or more field(s) which are required and hidden.
If any field is required and cannot be filled because it is hidden or invisible it will send a message saying that some required field(s) are not filled in.
To avoid such error, you would have to not set field(s) such as required.
If you want to have validation to your likings you could use a method I've developed for xfa forms with Livecycle.
There's plenty of explanation + a form with exemples.
Re: Resources for from design - best practices for layout?
With this practice you should be able to work with forms the way you want.
Another way without using the method above would be changing the required fields as the form follows. When a required field becomes hidden you should remove it's required property and set it to optional.
javascript - Adobe LiveCycle designer - form scripting - changing the field from optional to require...
Hope this will work.
