Hi,
have had the same error kind of out of nowhere. Here is what helped for me:
I have had FTP data in my wp-config.php. Since years. Didn’t raise an error till now. Hosting is by all-inkl.com (only mentioning it as someone else mentioned it elsewhere). After I removed the FTP credentials from wp-config errors just vanished.
Hope that puts you in the right direction too.
Cheers,
Sven
