It also seems that in R4 if there a field called "Form" then the stored form option in the form design is overridden, ie disabled. In R5 this is not the case, the Form field is ignored.
So if you are getting errors for R5 and not R4 , then check the stored form tag.
Are documents not appearing in a view which has a selcetion formula based on the Form field? This could be this problem.
If you manually set the form field then the document will reappear in the view.