Create a course, enroll everyone in it, create a forum with forced subscription, post the notice in the forum. When you're done and you're sure the cron has run...delete the course if you no longer need it.
Steve
Or just send a message from your Site News Forum (making sure that've forced everyone to be subscribed).
On my site, I actually have a special site-wide forum dedicated for such announcements as well as the 'Site News' forum. Everyone is 'forced to be subscribed' and I use it for ad-hoc low frequency announcements about scheduled maintenance, known problems, etc.
Thanks.
Met.
Ah, well that's a different issue
Ok, a number of variables here... the answer could depend on which version you are using, which operating system you have, whether cron is running, etc.
Is it just the Site News forum, or does it also happen with other forums?
If it does happen with all forums, then it's a bigger issue.
If it's just the Site News Forum, at a guess I'd say it was a problem with your 'front page roles' in 1.7 or 1.8. It's much simpler in 1.9 - but in 1.7/1.8, you need to allow students to take part in front page activities, which the Site News Forum is.
Have a look at the following links, which may be of help:
Hummm...imagine that...maybe I should write a book
Steve