This object class is already being used somewhere else, in a functions file or a theme or a plugin:
WP_REST_Navigation_Fallback_Controller
Suggest you disable all plugins, and Activate them one-by-one until you see the error, then you will know where the conflict is ocurring.
I am getting the error too:
Fatal error: Cannot declare class WP_REST_Navigation_Fallback_Controller, because the name is already in use in…….
I’m simply attempting to view a webpage (vital, as I need to attend a meeting today, and cannot access the site to find the time and street address from the needed wedbsite)
I tried disabling all plugins (I only use four) but to no avail.
My firefox is up to date, and I’m on windows 11 Home. Also up to date, and is always kept up to date.
The only other advice I am seeing elsewhere seems to suggest deleting various folders that I have absolutely no idea of what it all means.
I am not aware of anything wordpress, and unsure if it is something i use, although I have heard of it.
What should I do to resolve this?
Did you try a different theme?
Thank you for such a quick reply.
yes, I just tried disabling the only custom theme I use (dark)
But it hasn’t helped, I’m afraid.
And I just tried accessing same site on Opera browser (up to date)
Exactly the same error.
Might it be a fault their server end?
This has nothing to do with the browser.
As you can see from this link,
https://developer.ww.wp.xz.cn/reference/classes/wp_rest_navigation_fallback_controller/#changelog
this method was introduced into the WordPress core starting at v6.3
which means that while the method was available using REST, it was not in core.
In your particular case, the method is already being called in the Gutenberg plugin you have installed.
So you can disable this plugin. If you disabled this plugin and the error is coming from the same place, then suggest clearing your cache. The other option is to roll your WordPress core back to the earlier version prior to 6.3.
if you disable this plugin, and clear your cache, and the error remains be sure to post back the error to this thread.
Firstly, thank you oince more for your time and effort here.
Gutenberg plugin?
if it is installed, I certainly didn’t install it. I don’t even know what it is.
And wordpress? I only know that this website is called wordpress, otherwise I have no awareness of using it.
This is all alien to me, to be honest. Even though I’ve been using PC’s and laptops for decades.
So, I have to do all this for plugins and apps I never installed?
It’s very bewldering.
I just had a look at this page: https://ww.wp.xz.cn/plugins/gutenberg/
I don’t have a website, and do not edit any either.
Hence I don’t really know what wordpress or gutenberg are, nor do i use or need them.
I was simply trying to access a website via my browser, and got that error (and have now missed the meeting I was meant to attend).
And I can’t ”rollback” software I don’t use or have.
I just completed a full PC search with Everything (a deep search tool that can see everything on my device), and the only references to wordpress are just data relating to being on this site and logging in.
~As for gutenberg, I don’t have it anywhere on my device.
Hi @puzzledperson – you certainly are confused!
Accessing a random website, and seeing this error msg:
Fatal error: Cannot declare class WP_REST_Navigation_Fallback_Controller
has nothing to do with your PC, or laptop, or your internet. It simply means that the website you are trying to access is inaccessible, and the owner of the website needs to fix it.
I figured that much out by myself.
So, why was I given all that advice about gutenberg and rolling back wordpress etc, when, reading back my messages, it seems obvious I dont use the website editing tools or gutenberg? And had already checked my plugins before beign advised of gutenberg.
The confusion appears to have been handed to me. lol
I found another website related to the organization, and it didn’t give the error. It just simply couldn’t load. And then I found a phone number, and the sites are apparently down now. (luckily I can join the next meeting though)
But, yes, any time I did a websearch to find out what was wrong, all I could find was advice resembling the same that you gave me earlier above, which had no baring upon my question at all. (not being a wordpress website builder or editor, and simply trying to load a webpage)
reading back my messages, it seems obvious I dont use the website editing tools or gutenberg?
Clearly, I disagree! It was not obvious.
”am not aware of anything wordpress, and unsure if it is something i use, although I have heard of it.
What should I do to resolve this?”
”I just completed a full PC search with Everything (a deep search tool that can see everything on my device), and the only references to wordpress are just data relating to being on this site and logging in.
~As for gutenberg, I don’t have it anywhere on my device.”
”So, I have to do all this for plugins and apps I never installed?
It’s very bewldering.
I just had a look at this page: https://ww.wp.xz.cn/plugins/gutenberg/
I don’t have a website, and do not edit any either.
Hence I don’t really know what wordpress or gutenberg are, nor do i use or need them.
I was simply trying to access a website via my browser, and got that error”
It is clear I do not use worpress website editing tools, not gutenberg.
@corrinarusso Thank you for your help. I am also having this problem. I disabled all plugins, moved the gutenberg folder out of its current location, flushed the cache through siteground but still cannot access my admin account. Any other suggestions?
Well ………… login to Siteground, and use the file manager to zip up all your plugins, and then remove *all* the plugin folders out from under /wp-content/plugins/
Start there. Next would be to do the same with /themes/ – but leave a default theme there.
Just noticed this same error on a small WP install we use for our blog. I haven’t found a solution yet, but I will post if I find one.
