PHP fatal error when switching the theme

I got this error when I switch the theme:

PHP Fatal error: Uncaught Error: Undefined constant "USER_SWITCHING_OLDUSER_COOKIE" in /wp-content/plugins/user-switching/user-switching.php:1352
Stack trace:
#0 /wp-content/plugins/user-switching/user-switching.php(490): user_switching_get_olduser_cookie()
#1 /wp-content/plugins/user-switching/user-switching.php(542): user_switching::get_old_user()
#2 /wp-includes/class-wp-hook.php(307): user_switching->action_admin_bar_menu(Object(WP_Admin_Bar))
#3 /wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#4 /wp-includes/plugin.php(524): WP_Hook->do_action(Array)
#5 /wp-includes/admin-bar.php(95): do_action_ref_array('admin_bar_menu', Array)
#6 /wp-includes/class-wp-hook.php(307): wp_admin_bar_render('')
#7 /wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters('', Array)
#8 /wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#9 /wp-admin/admin-header.php(267): do_action('in_admin_header')
#10 /wp-admin/admin.php(239): require_once('/Users/...')
#11 /wp-admin/plugins.php(10): require_once('/Users/...')
#12 {main}
  thrown in /wp-content/plugins/user-switching/user-switching.php on line 1352

I’m activating the plugin on after_switch_theme hook, like this:

function theme_init() {
    include_once( ABSPATH . 'wp-admin/includes/plugin.php' );
    activate_plugin( 'user-switching/user-switching.php' );
}
add_action( 'after_switch_theme', 'theme_init' );

Here’s the scenario:

• Setup a fresh install of WordPress.
• Delete the default themes from the themes directory.
• Upload the custom theme to the themes directory.
• Login and navigate to Appearance -> Themes.
• Activate the custom theme.
• You will get the error.

This error disappears when you refresh the page, it appears only for one time after switching the theme.

• This topic was modified 2 years, 2 months ago by abazeed.
• This topic was modified 2 years, 2 months ago by abazeed.
• This topic was modified 2 years, 2 months ago by abazeed.