Litus Mod does not alter any native armours, all of its armour additions have been 'stacked beside its original counter-parts'. There are only a few reasons why this wouldn't work with Litus or any other modification that may include new armours and items.
BRF additions (all BRF's located in a resource folder must be linked via the .ini file as load_mod_resource = (enter name) if you've updated any native brf files and left them in the native 'commonres' folder then thats the problem. I copied the brf's I edited in Litus and added them to my module so that it reads the brf's from Litus and ignores the brf's lcoated in the commonres folder. Armour issues are usually the result of a brf problem.)
Items_Kind1 file (adding new item entires where we have new entries directs in an error/or replacement. I doubt this is the case since it works fine with 1257 ad)
I'm guessing..it's the brf. I think we both edited the same brf and Litus is ignoring yours which is in commonres and not the module - resources folder. (I havent downloaded to check though) you can fix this fairly easily by renaming any of the brf names and simply adding it's new entry to the .ini file.