White screen of fatal error

Hi Alan

This error comes up when a specific function is created more than once. The function in this case is called sdec. There isn’t a function by this name in the default file /wp-includes/vars.php – so it’s possible that something has modified your files.

One cause might be another plugin injecting this code into that file. It’s also possible that this is a malicious plugin, so I’d start by deleting plugins that you’ve downloaded from untrusted sources.

Here is a temporary solution for your particular case.

https://wordpress.org/support/topic/fatal-error-cannot-redeclare-sdec-2