Ok, so you’ve updated the plugins and themes and the error shows up.
This error means that you try to use function that no longer is defined.
Most probably it was defined in a plugin and the newer version changed its API. And your theme (or some other plugin) is still using the old API.
So how to fix that?
- Download your code.
- Search for occurrence of that function call and
locate all of them. - If they’re located in your own code, modify it to
use current API. - If they’re in third party code – notify their
authors and wait for fixes or stop using them.