Plone site won't allow me to log in with zope users created with bin/instance adduser

I usually create new zope users on the command line using a command like this:

 bin/instance adduser myadmin newpassword

I've inherited a site which, seems to create new users but then I can't log into Plone with those newly created Zope users. Why might be the cause for this?

the site in read-only mode?

can you dig into the site using "debug" and make sure the emergency user is actually created? Very odd.

I see at least one potential reason:

"adduser" adds new users to the root "acl_users", not the "acl_users" of the Plone site. Special configuration may prevent those users to be able to log in in the Plone site. Do not use "adduser" to create new Plone users (but only Zope-"Manager"s)

That makes sense.
As this is a site that I've inherited my best bet, if I want to log in, is to be able to write to the acl_users of the Plone site. I started to attempt that but I'll try it again now that I'm pretty sure that is the issue.

For Plone Versions 3.x and 4.x:
I also had this 'not-being-able-to-login' to plone site with credentials from an account created by buildout (user=username:password).
It seems like you have to create a Plone site first before being able to log in to the site and others, for example imported Plone sites besides the one created in ZMI.

This is a much better way of creating emergency users than what's documented in which points to

Thanks @pigeonflight ... you saved my (Canadian) bacon! :canada: :bacon: !!!!

Glad to be of help.