SOLVED
After more persistent searching of the forums, I have finally found the answer so please ignore my post below.
So simple..the rails and profiles must be identical to produce square "Holes" using Lattice Maker.
Sorry for not finding that before posting..

Hello..I have searched the forums but cannot find a solution to my blundering attempts to create this:-

Using EEbyRails and following the instructions (also have tried every combination of those)and then Lattice Maker, the result i always get id this:-

No matter what I try, I cannot create the "Square" holes, only triangular ones.
If I remove the triangular lines prior to using Lattice Maker, the faces disappear making Lattice Maker not function.

Any help would be greatly appreciated ..
Thanks..