There is a new message in the "messages.yml" file. This message tells the user what the valid Bar IDs are, and it is sent when they try to open a bar with an invalid id.
You must either regenerate your messages.yml file, or add the following lines manually.
Code (YAML):
# Sent to players when they try to open an invalid bar # %idList% = the list of valid bar IDs validBars: "&fThe valid bar IDs are &c%idList%&f."