Capacity Exceeded message

We use the standard Room and resource reservation template and allows people to reserve rooms through their calendar. If the reserve a room more attendees than the capacity they get a reply “WARNING! Capacity Exceeded:” .

The message is correct but it confuses our users. I would like to change the message but haven’t found out where it’s stored. I’ve searched the design of Rooms and resources but can’t find it.

Do you know how to change the message?