"Missing required dependencies"

A few people who have tried to use my Celtic civs pack have been encountering an error when trying to load the mod where it says that they don't have all the required dependencies, even when they do have all of them (these are BNW, G&K, Denmark and Wonders). I have not noticed this error when using the mod and there a plenty of people who seem to get it to work fine. Is there something that would cause such an error, or are the people reporting it just making a blunder of some sort?

Bumped. I'm still getting people reporting this issue can I can't work out what is causing it. It's happening with several of my mods apparently.