We have found that if you put the female in the shouldered Lamello slot of your vertical parts, and the male in the shouldered Lamello slot of your horizontal parts, they do seem to go together easier.
You also want to make sure that both the male and female Lamello's are not in the slot uneven (make sure they are pushed in far enough that the face of the Lamello is on the same plane as the face or edge of your part, centered and level). If the female is in crooked, when you go to push the parts together, it will slide even more in the direction that it was out, and it will become impossible to snap the connectors together.
If you accidentally do put a Lamello in incorrectly, and you can't snap it together, if you have put a significant amount of force trying to push it together, it is best to disassemble, and then replace the male part (it is almost impossible to damage the female part, but the tines of the male part are fairly easy to damage).
UPDATE: We now insert the Lamello fasteners for you. When you receive your Cabinotch Full Access project, all fasteners will be pre-installed.
You also might find our Blog post on Full Access Assembly useful.