Valid from List & Label 8
If List & Label is run within a service you might encounter the return value -11 from LlPrint[WithBox]Start and other functions. This value, LL_ERR_NO_PRINTER occurs regardless of the number of printers installed.The cause of this behaviour is that the SYSTEM account used for services by default does not have access to the installed printers. List & Label needs access to a reference printer driver, even for preview and export.
See the following link that deals with this issue and describes how to install printers for the SYSTEM account. If you proceed as described there, you should be able to print from your service.
Please note that you need to purchase separate server licenses in order to run List & Label within a service.
Links:
https://support.microsoft.com/en-us/help/184291
IDKBTE000571 KBTE000571