Hi guys, based on the commented error, I confirm one of the solutions indicated here as well. We recently had a customer with a similar problem (windows server 2016)
License check failed. Try 1 out of 5. Request to ESET Endpoint Security/Antivirus failed. Error PERSEUS_E_EI_NO_LICENSE (21801)
The EI was not showing activated despite having an active license.
Checking thoroughly, this client had a license renewal which still did not show up to date. What was done in this case was to uninstall the ESS and then the EI on that computer, both were reinstalled and by jointly reviewing the installer log it was possible to verify that it was activated without problems and the error did not return. In this particular case, the client had EP v10/ ESS v9 and EI v1.9.