I've been reported that sometimes this error shows up for admin:
PHP Code:
Fatal error: Class 'VBMAIL' not found in /home/..../public_html/forum/dbtech/vbmail/hooks/mail_send.php on line 10
I traced it a little and noticed it could only happen during vb cron mailing. You include the class in "global_bootstrap_init_complete" hook so it should be there in all page visits but there must be a vb section which triggers vb mail cron for admin visitor without initializing "global_bootstrap_init_complete" hook to produce this error. I'm still working on it to find where but wanted to report here in case you also have an idea.