cannot login one site only multisite subdirectory install

You have had a plugin bjork up the user roles/capabilities on that site?

I would continue to troubleshoot via phpmyadmin:

First, figure out the site_id of the site and a user_id of an administrator of the site.

Now, browse the db – wp_usermeta – for the user_id that is a member assigned as an administrator to the “n” site_id.

You should see something like:

wp_n_capabilities = a:1:{s:13:"administrator";b:1;}
and
wp_n_user_level = 10

If you spot something different, note it. But it sounds like you looked already.

Next, browse the db – wp_n_options .

You should see something like
wp_n_user_roles = a:5:{s:13:"administrator";a:2:{s:4:"name";s:13:"Administrator";s:12:"c ............

Now I would compare carefully the wp_n_user_roles there with the wp_x_user_roles of a site where all is well.

Another place is to edit the site via the Network Admin->Sites-Edit and add a new/existing user with a role there and see if something “burps”.

Might you have a theme active – with some function/plugin there bjorking it up – on that site different from the rest?

I’ll try option 2 — I tried granting a new user access and that failed to let me in.

Is there somewhere I can uncover the meaning of these cryptic codes (s:17, b:1, etc)?

I thought of the theme function idea; but several working sites use the same child theme; The comparison of a working user_roles with the non-working one didn’t turn up anything thing other than a couple of rights for plugins present in a working site, but not present in the broken site.

Interesting — if I clear my cookies in the browser, I can get the wp-login.php page; but when I try to login, I get the error message; And, thereafter I get the error message and no login page;

I think I have it fixed — well sort of. I found 2 plugins that were updated in the last 2 days; I had to move them out of the plugin directory; then I updated the network, and I can get back in to the site.

Now, to figure out which of the 2 is the problem.

Here is a link to explain php serialize, but that is more than you need.
https://ca1.php.net/serialize

Your original post suggested you had disabled plugins, but how did you find two more?

Swap out your plugins … anyway, when you find the one, and can reproduce the error – you can post in its support forum specifically.

Other trouble shooting tips:
https://codex.www.ads-software.com/Login_Trouble

David: I had disabled all plugins specific to the problem site [this multisite hosts about 10 production sites, and I was trying to avoid breaking the other sites]. I found 2 plugins that were enabled on multiple sites but which had been updated between the time I could login and the time I could not login. I had to move them out of the plugin directory to disable for the site.Then I could then login to the site.

I proceeded to reactivate these plugins, first by putting them back into the directory, and then activating on the site. Now, plugins are activated and I can login to the site. So, now I do not know which plugin (or combination of plugins) caused the problem since I could no longer break the login.

I think I’ll call this resolved — source of problem not solved, but issue itself resolved.

Thanks for the help and links.