Please log into the server files on the Files > FTP File Access page of your control panel (same password as your MultiCraft account to log in) and delete the jar folder - then restart the server. This will force reinstall the modpack which should resolve the issue.
Literally what I said resolved their issue 3 years ago. If you actually have the issue, and are not just posting on another very old thread for no actual reason, do what I said above - if that doesn't work then send a ticket in about it.