1. Check the version of the game and the version of the mod. If necessary update the game and the mod to the latest versions.
2. Try to delete all other mods from the Mods folder except NPCC. If the problem disappears then it is a mods conflict. You need to find a conflicting (or outdated) mod within your Mods folder and remove it.
3. If NPCC Mod alone causes an error, check whether the file lastexception.txt has been generated at your The Sims 4 folder. If yes, post its content or upload it somewhere and post a link.