I have been able to replicate such an error message if the directory structure ends ups looking like this mods/mods/adult-content but it should be mods/adult-content
Which form of patching did you use, the exe or the zip file?
I believe this can happen if you unzip into the mods folder instead of the game folder.
Viewing post in Star Knightess Aura Patch comments
I'm not sure how it happened,
but I believe the issue is that all those files should be in a folder called "adult-content" in the mods folder.
EDIT: I have updated the description for using the zip file so it's clear one only has to unzip the file into the game's Steam folder. No more manual copy&pasting after extraction necessary!