Error cannot open tty-output Linux

Question

I have installed a paravirtualized Debian8 image on Xenserver, and I am adding a script to create a template for this vm. I added the script on startup with the command "systemctl enable script". In the scritp I use the dialog that is already installed.

When I convert vm to template and create a new vm, in syslog log I get the following error as if the script had started at the wrong time of boot:

initial-conf[407]: Error opening terminal: unknown.
initial-conf[407]: cannot open tty-output
initial-conf[407]: Error opening terminal: unknown.