Cannot turn off Developer mode - "managed by your organization"

Bree said:

Yes, that seem the most likely explanation. Take it back and ask for it to be replaced/fixed?

It will probably come to that if this can't be fixed. It was an Amazon purchase, so I hope they cooperate if it needs to go back. Thanks!

Brink said:

That would most likely be why unless something else is set.

Deleting the DWORD value and restarting the computer should hopefully sort it.

Brink, you are a miracle worker! After weeks of struggling with this, your suggestion worked. That "AllowAllTrustedApps" subkey was the culprit. I went in baby steps and first changed the value to 0, which caused the checked box to move to Windows Store apps, and all three options in that section became grayed out, but "managed by organization" remained. Then I deleted the entire subkey, restarted, and that annoying notice was gone! What a relief! I'm ecstatic.

I'm sending you boatloads of good karma. You had the winning solution. THANK YOU!!! I very much appreciate the help of everyone here who attempted to sort it out. Thanks to all of you.