This is acutally related to WeiDU, and not the Kelsey mod itself. What you need to do is update the WeiDU program, and to do so, you have to figure out which mod has the most recent version of WeiDU. Run the steup of the most recent mod, and it will then update all the other older WeiDU setup's of the older mods (I like using Xan to do this, he has WeiDU 199, which is close to being the most recent if I'm not mistaken). Just make sure you don't touch any of the components in the mod you're using to update the WeiDU, so as not to mess up your mod install order.
As an example, say that you want to install Ascension (WeiDU N°176), then Kelsey NPC (WeiDU N°153). First, you have to install Ascension, than you try to install Kelsey, but get that error message that disappears. You then run the Ascension setup program, it'll update Kelsey, you exit, and go back to the Kelsey to install him.
I hope I'm making some sense!
It's not exactly a simple method, but it's the only fool-proof method I've found so far. Hope this helps!