Hey,
If my memory serves, you've got to run the Mod changer at least once before you run any other mod. This gives the Mod Changer the chance to learn the baseline configuration (in this case 2.5.5.2).
AFTER that, close the Mod Changer, and then install the first Mod, THEN run the Mod Changer again, it should detect it this time.
Let me know how that goes.
-Strat