This seems to have been resolved with the latest updates to the parser. On the 
attached instance, we get a meaningful error:

error: duplicate object 'filter'
please check :constants and :objects definitions

I close this issue as resolved.

I think the problem is that there are two objects named "filter" -- one as a
constant in the domain file, another as an object in the problem file.

It would be good to make the translator catch multiple objects with the same
name during/after parsing and report that as an error. Somehow got time to
implement it?

Bug reported by Bob.

In the attached problem, the translator reports "Simplified to trivially false
goal!" and generates an unsolvable task. However, the task is solvable. In
particular, the problem goes away when commenting out the (useless) negative
effect "(not (free ?iter))" in the first action.

Malte, feel free to add to nosy whoever you think appropriate.