error message at top of admin screen, and bulk updates result in "page not found

Try downloading WordPress again, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, and delete then replace your copies of everything on the server except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings.

Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.

I’ve already done that with no change in outcome.

Is there any difference with the Twenty Sixteen theme active?

Yeah, the message doesn’t appear, but I’m still unable to update plugins. This is a multisite install, BTW, although at present I only have one site active.

Since it does appear to be a theme issue, where would I start to look for the problem? I’ll contact the theme’s support forum (it’s a purchased theme) and see if they have any solution, but it some times takes a while to get a response.

Thanks.

Ok, in the future please post your support requests to https://www.ads-software.com/support/forum/multisite as Multisite Networks can be very different in key ways. (I have moved this thread for you.)

Is the affected site the primary site, or one of the subsites?

It is the primary site and the only one that currently I’m using.

Are any of the subsites affected?

I tried to access the other site that I currently have as a subsite from the network dashboard, but got a 404. I’m able to access the site’s front end by using its domain name, but am unable to access its dashboard.

I thought it might be due to the multisites plugin not being activated (I have all plugins currently disabled), but that got the same error that started this thread and nothing else. That is, the only thing that appeared on the page was the error message.

I checked the .htaccess file, and it appeared that the hosting company had reverted it to the basic file for WordPress, so I looked through the backups and found what I thought might be the correct edition. I changed the file to:

# BEGIN WordPress
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

# END WordPress

This resulted in the elimination of the error message at the top of the admin dashboard, but everything else remains the same. That is I can’t upgrade plugins and I can’t get to the subsite dashboard.

This is using a default theme, BTW. If I switch back to my normal theme, I’m back to the error message at the top of the dashboard.

Hm, ok, so I’m going to guess that’s related. ??

My Multisite knowledge is about 7 years out of date, so I’m going to see if I can poke someone else to take over before I suggest something that leaves your network in ashes.

It has been suggested that this sounds very similar to a bug which is fixed in WordPress 4.6.1.

The official release is planned for September 7, but if you’re eager to apply the fix now, the release candidate is now available: https://make.www.ads-software.com/core/2016/09/01/4-6-1-release-candidate/

4.6.1 is officially out now, would you please upgrade to that and see if there’s any improvement?

WordPress 4.6.1 Security and Maintenance Release

I tried this, but there was no change.

The issue turned out to be a function in my child theme.

Awesome, I’m glad that’s out the way now, and thanks for letting us know! ??