Fatal error when trying to access backend in /.../lib/settings/podcast.php

I have been experiencing the fatal error when trying to access the backend of my page:

“Fatal error: Call to undefined function Podlove\Settings\register_setting() in /www/htdocs/w01400c7/follow-up.fm/wp-content/plugins/podlove-podcasting-plugin-for-wordpress/lib/settings/podcast.php on line 35”

I guess there could be some connection to W3 total cache which is a b**** of an addon, at least for newbie users like myself. At the moment I seem to be forced to redo my pages completely :-/

Anyhow, this error above is keeping me from my backend - any ideas?

EDIT: Deactivating Podlove by renaming directory changed the error: “Fatal error: Call to undefined function register_setting() in /www/htdocs/w01400c7/follow-up.fm/wp-content/plugins/podlove-subscribe-button/podlove.php on line 61”

A short note: W3 ist not (yet) compatible witch Wordpress 4.7.
Could this be a hint?

Might be a way to find the solution - I am not able to, though.

I’ve managed to gain access to the backend by deleting plugin files and editing the database (active plugins in the options table). After that, I was able to filter all malfunctioning plugins (including W3) and deinstalled them. I also was able to fix the 404 error in nearly all links.

So at the moment, the site is running - without any podcasts, though. Reinstalling Podlove or the PL Subscribe Button reproduced the error (backend inaccessable, error message in Line 61).

Anyone have an idea how I can fix this?

EDIT: Both lines with errors use “register_setting”…