I'm guessing you're using a caching plugin such as WP Super Cache?
Do you use cpanel to host your site? You should be able to go into your files, and then navigate to the path that it indicates, and delete that file. Then you can import your existing site. Sometimes this can occur when you've used too different caching plugins, and they've both generated the advanced-cache.php file. Simply, duplicating copying it from the main plugin you intend to use to the other location should do the trick.
Yes, I have this plugin and and cPanel. I already previously moved my website from old host to current one. I was a bit afraid t go into files myself to screw something because my knowledge is minimal. But I tried to find this file. Now I deted this file and error had disappeared. Thank you so much for your help!