Want to downgrade, foiled!

[CurtCharlesPDX]

I had rooted an S4 running 4.4.2 with NC5 and it was swell. Then I took the OTA (will I never learn?) and it a) un-rooted, and b) installed NG6. Sadly, it took a factory reset (home, vol dn, pwr) to restore the phone to proper function. Now I get a "security warning" every 10 minutes, and WiFi passwords aren't retained. If I turn WiFi off, I have to do a "Reset Settings" to get WiFi back on again.

What I want to do is re-flash NC5, root it (with TowelRoot), then re-flash with NG6 just to avoid the daily "update your phone" hassle.

I have installed Odin 3.09, and have the ROM images for NC5 and NG6. I have the Samsung USB driver installed.

I boot the phone into download mode (home, vol up, pwr) and note a message that reads "Write Protect: Enabled".

I connect the USB cable and Odin recognizes the connection. I select the MD5 for NC5 in the AP (PDA) and Odin verified it's checksum. When I click "Start", Odin does the download (progress bar) and reboots the phone, showing "Reset!" in the status box.

When the phone comes back up, two things are noted:
1) It runs for a couple minutes, then re-boots. Repeat until battery remove and factory reset.
2) It still has the NG6 ROM; the NC5 does not appear to be active.

I'd appreciate any assistance and advice the community can provide!