What version of CWM are you using? You said you had been using CM11 so you are probably using too new of a version. You need a version older than v6045 to flash the plain stock zips. You can get the older versions at my HD/HD+ CWM thread linked in my signature.
Sent from my SM-T900 using XDA Premium HD app
See my Nook Color Tips Thread here
and my Nook Color EMMC Partition Repair Thread here
and my Nook Color Updated CM SD Installation Instructions here
and my Nook HD/HD+ stock tips thread here
and my Nook HD/HD+ CWM Root Tools thread here
e.mote's Nook HD/HD+ Dummies Guide for installing CM10.1/CM10.2/CM11 here