I would like to turn off the option that allows invited people to post on a Facebook event's wall. I want to restrict it so that only hosts can post. How can that be done?
Events created by Pages have an option to allow only the page admins to post to the event wall. When you create the event, just check the box next to "Only admins can post to the Event wall." If you've already created the event, you can click the Edit button at the top right and you'll find the checkbox at the bottom of the edit window.
Events created by individuals and groups do not appear to have this option available.
As of now there doesn't seem to be any way of restricting users posting on the events wall. I faced this problem a while back too.. But as a host you can always delete unwanted post/comments.
Here's a possible work-around - why not create a FB group instead which offers better control. Then invite all members to an event but you will have to request them to not post anything there.
Take a look at Events - Facebook help center, for more details. You could drop in a suggestion to FB too :)