how to fix that ?

 

Have you done what it says already?

Have you upgraded yout site? Is the adblocker plugin ready for your current version?

Have you tried deactivating/reinstalling that plugin?

22 minutes ago, opentype said:

Have you done what it says already?

Have you upgraded yout site? Is the adblocker plugin ready for your current version?

Have you tried deactivating/reinstalling that plugin?

i  am delete the plugin and site show that alert , how to restore defult theme?

Cleaning the cache with “Something isn’t working correctly” in the Support section normally should be enough.