I was thinking it was the importer, since that would change the structure of the NPC node within the db.xml if it was setup to output a different structure. I didn't see that. You could load each one till you get an error to find out which one is the issue and report it to the developer. I would do this with a throw away campaign. There is always risk of issues like this with extensions as base ruleset code can change and the developer has to make those changes to compensate.
EDIT: Based on Trenloe's response, you can still keep your original campaign and just unload the module. I would reach out to the developer for that module and inform them of the issue.