[Deprecated] DMZ 1.5.3 (DataMapper OverZealous Edition)

[eluser]OverZealous[/eluser]
I don't think the error is not being caused by the two lines. When you comment them out, the $save below them just doesn't attempt to save the Category. The error message explicitly mentions Article, so the error is most likely related to Article.

Do you have a controller that is also named Article?? You cannot have controllers with the same name as your Models (otherwise one class will override the other).