Fatal error: Call to a member function add_query_var() on string

You need to check your plugins. If they are not compatible to the current WP version, deactivate them. Keep doing that until that error goes away.

Once you find the culprit, check to see if there is an update version of the plugin. Otherwise, you will need to find something else.

I hope this helps.

I tried removing plug-ins and that did not work

‘removing’ or did you deactivate them? I would deactivate all the plugins for the time being to see if that resolves it. If not, then switch themes to one of the default ‘twenty*’ theme.

If the problem persist, reinstall WP 4.9.1.

@ouch

Is that the full error message, there are often two parts to it.

1. The message from Core (As you have noted here).
2. The message of the errant plugin or theme.

Part 2 tends to be much more useful when troubleshooting.

I changed the theme, dactivated plug-ins and I am still getting the error on this page:

https://www.deerrepellent.org/

Is it possible you didn’t deactivate all plugins? Did the site lock before you got a chance to deactivate them?

If that’s the case; you’ll need to go into your site database (via phpMyAdmin); go to the wp_options table and delete the option active_plugins.

This will manually deactivate all plugins; and may allow your site to load properly.

NOTE: You may want to take a database backup first; if you’re at all inexperienced with database management.

• This reply was modified 7 years, 3 months ago by Josh.

I only have 3 plugins. I deactivated all of them. I went to the wp_options table and active_plugins was not there.