Warning: is_writable() and Warning: Cannot modify header information; errors

I just automatically upgraded my WP after a period of inactivity, and now when I try to update a page I get these two messages:

Warning: is_writable() [function.is-writable]: open_basedir restriction in effect. File(/) is not within the allowed path(s): (/home/user123:/usr/lib/php:/usr/local/lib/php:/tmp) in /home/user123/public_html/blogfolder/wp-admin/includes/misc.php on line 128

Warning: Cannot modify header information - headers already sent by (output started at /home/user123/public_html/blogfolder/wp-admin/includes/misc.php:128) in /home/user123/public_html/blogfolder/wp-includes/pluggable.php on line 865

Neither impede the actual publication of my changes, but it’s very annoying having to re-navigate to the admin area manually each time. I’ve looked through many topics on the first error, and have followed every instruction I found, but none are successful. I’ve tried the official solution to the second error, but removing excess whitespace (or whatever the “delete button” method is for) didn’t work either. I figure the errors could be coming from the same place, or have similarities because they both involve the misc.php file.

Please don’t just refer me to a search query or previous topic, because I’ve checked thoroughly through them and can’t find anything that works. I’m not the most tech-savy person around when it comes to PHP, so a little guidance would help immensely.