As suggested I am copying here some suggestions from David Lieste regarding the minimum things you must have in order to get an Estab to work.
I don't *know* for sure, but my experience with problems with new Estabs leads me to the following conclusions:
You need two sides, with at least one "Nationality" and "Army" on each side.
Each "Side" seems to need at least one line unit, one base, one support unit and two HQ echelons (eg for Coy units, Bn & Rgt HQ).
Each "Side" "Nationality" and "Army" should have the two 'flags' as actual designated images (they can all be blank &/or the same), *null* while a valid type seems to cause problems in one Estab that I have tested before (not confirmed, but an easy one to avoid discovering the hard and obscure way).
Every unit must have at least one weapon. Unarmed units are not allowable, the weapon must be 'effective' but it can be of trivial usefulness.
Every weapon must have at least one ammunition nature assigned (most to APers), and there needs to be at least one entry in the range/effectiveness table, there are a maximum of 6 entries, although it will appear to take more it won't be valid.
Supply units must exceed a minimum strength in personnel, and have suitable transport (waggon or pack-mules/packs). IIRC this minimum strength is around 20 men, but it might be higher.
Hope some of this helps, but it is tricky setting up a new Estab, and there are lots of pitfalls ~ this is a bit beyond what the tools are really 'released for' - they are somewhat unpolished 'internal' tools intended to allow the community to do a bit more than 'just' change the map and participating units, and to add new elements to the existing DB..
On the plus side, the tool is easy to use once you have a working DB for adding and changing details.