Can't check categories when add new listing


Still straggling with translation… Having one problem and one question…
The problem:
When I get into "add new listing" as subscriber – I can't check categories. (no problem with admin).
I had been trying to find out how come it's working just fine, and then, suddenly, I can't check categories anymore…
I had installed directory plugin few times (wp 3.5.1, directory 2.2.2).
I had tried to isolate every single step…
Finally I found that after getting into CustomPress – Taxonomies tab – listing_category – trying to translate something, or even without translating, just saving…
This happens (that I can't check listing categories as subscriber).
Any idea? Maybe this one is for Arnold?

The Question:
Where do I translate error message: "This field is required" (add listing page)?