DError with plugin and pluggable.php

Hi all.

I have a problem with this plugin, that seems to be messing with my system. I can’t log into my account anymore, receiving only this:
Warning: Use of undefined constant SECURE_AUTH_COOKIE – assumed ‘SECURE_AUTH_COOKIE’ (this will throw an Error in a future version of PHP) in /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php on line 923

Warning: session_start(): Cannot start session when headers already sent in /www/htdocs/w01253c6/wordpress/wp-content/plugins/visual-products-configurator-for-woocommerce/admin/class-vpc-admin.php on line 125

I went to my FTP and deleted the plugin folder. Still, I am having trouble not being able to log in anymore. Now all I get is the following:

Warning: Use of undefined constant SECURE_AUTH_COOKIE - assumed 'SECURE_AUTH_COOKIE' (this will throw an Error in a future version of PHP) in /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php on line 923

Warning: Cannot modify header information - headers already sent by (output started at /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php:923) in /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php on line 1416

Warning: Cannot modify header information - headers already sent by (output started at /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php:923) in /www/htdocs/w01253c6/wordpress/wp-includes/pluggable.php on line 1419

So thinking it might be the pluggable.php file, I went and replaced it with the file from my wordpress download (shouldn’t be messed up).

Does anyone have any thoughts? I host 3 websites on the account, one is down completely, the others still accessible to view, but not pretty.

I really don’t have more ideas.
Any thoughts anyone?

Much appreciated!

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