Fatal Error encountered when trying to customize site

Fatal error: Call to undefined method WP_Customize_Manager::register_section_type() in /home/financ45/public_html/testsite/wp-content/themes/sydney/inc/upsell/class-customize.php on line 68

the home page will load briefly but this is what I get when I click the customize button.

Can you help?

Also - I get this error when I attempt to import the demo data:
Warning: array_reduce() expects parameter 1 to be array, null given in /home/financ45/public_html/testsite/wp-content/plugins/one-click-demo-import/inc/Helpers.php on line 538
{“status”:“afterAllImportAJAX”}

Hello @emmacarter,

Please try to reinstall the theme. But please make a full site backup first.

Kind Regards, Roman.

Hello there,

I can’t reproduce the same issue on my test site. Could you please confirm if you have been running the latest version WordPress?

Regards,
Kharis

I will try to reinstall the theme and see if it works - but I am not running the latest version of WP - I am running 4.1.15

Do I need to be running the latest version?

Hello there,

We’d recommend you run the latest version of WordPress as based on the error message you’ve shared, the register_section_type() method isn’t available in the older WP version you’ve run.

Regards,
Kharis