error line 365

Thanks for reporting.

We are trying to recreate this warning at our end. Can you please explain steps when you are getting this warning?

I am sure this is not for admin.

was creating a new user account via the login page.
completed all required information and submitted. returned to the home oage with that message across the top of the page.

User was created.and received a website generated confirmation for Subrcribe2 as normal.

We again tried it with subscribe2 but no luck. we haven’t received such warning.
though I will suggest you (if you can play with code and files) to please go to /plugins/wp-email-users/ directory >> wp-email-users.php file line no. 365 and replace line

array_push($to, $useremail);

with

if(is_array($to)) {
	array_push($to, $useremail);
}

Hope this resolves your warning.