I think my code is almost the same:

(ns caiba-data.nrepl
  (:require [mount.core :as mount :refer [defstate]]
            [clojure.tools.nrepl.server :refer [start-server stop-server]]))

(defn start-nrepl []
  (start-server :bind "0.0.0.0" :port 7888))

(defstate nrepl
  :start (start-nrepl)
  :stop (stop-server nrepl))

BTW, If I just use start-nrepl, it works fine.

the exception is coming from db.clj line 13

what is that line, and do you have requires in that namespace?

if you can create an example (with all ns involved) that I can look at, it'll be easier for me to help