How do I change error messages
 

The way I have my board set up, people need to PM me to request access to post to the calendar / events forum. The only way to let them know this, however, is to post an announcement about it but you guys know as well as I do, people rarely read those. Is there a way to edit the error message people get when they attempt to post to the calendar so that I can say in that message that they must PM me for access? I've done a search in the phrase manager but haven't had any luck finding error messages. When people try to post, the system says they get the "No permissions" message.