Retro-fitting RNS-E and having CD changer problem...

I've just fitted a Mk2 RNS-E to my car along with a 6 disc CD changer in the glovebox, which replaced a Symphony II+ head unit and glovebox iPod connector.
Everything seems to be coded correctly and I've got the RNS-E unit showing the CD changer as being empty or full (all 6 disc slots are showing) , but when I try and play a CD in the glovebox changer the RNS-E unit just says "loading" and no sound is heard.
Any ideas please?
Thanks

Thanks for the reply.
I can't remember if I did that but I'll try it......