It seems like your installation was not done properly. Right now it looks like there are some missing reference files in the /etc/zbp directory.
I would just recommend to backup your /etc/zbp/data.db file and then reinstall the zbpserver. Here’s what you will need to do:
1. backup you current devices: $cp /etc/zbp/data.db /home/pi/
2. uninstall zbpserver: sudo apt-get purge zbpserver*
3. check the zbpserver repo, it should be:
deb http://repo.smartenit.com/v2 raspbian/stable main
$sudo nano /etc/apt/sources.list
4. install zbpserver: sudo apt-get install zbpserver*
5. restore your devices: cp /home/pi/data.db /etc/zbp/data.db
6. restart your service: sudo sevice zbpserver restart
Please let me know how it goes.