Site Not Loading – Warning: Creating default object from empty value error

I’m having trouble with my site loading…sometimes it does and sometimes it doesn’t. When it does it’s very slow. I think the trouble began when I was trying to update my header using the header image uploader. I just found these error messages at the top of the site and bottom:

Warning: Creating default object from empty value in /home/savingby/public_html/wp-includes/user.php on line 660

Warning: Creating default object from empty value in /home/savingby/public_html/wp-includes/user.php on line 660

Warning: Creating default object from empty value in /home/savingby/public_html/wp-includes/class-wp-admin-bar.php on line 167

Warning: Creating default object from empty value in /home/savingby/public_html/wp-includes/class-wp-admin-bar.php on line 167

Warning: Creating default object from empty value in /home/savingby/public_html/wp-includes/class-wp-admin-bar.php on line 167

Does anyone know what they mean or what I need to do to correct this?

Thanks so much!