The most likely reason is exactly as the message suggests. You should check that Sql services are running as expected.
Otherwise these McAfee support articles are worth review (checks and worarounds listed are valid for ePO 5.0 even though labelled ePO 4.5/4.6).
KB76582 - The license for ePolicy Orchestrator is invalid (When accessing the ePO 4.5 / 4.6 console page)
KB66166 - The license for ePolicy Orchestrator is invalid (when accessing the ePO 4.5 log on page)
KB78686 - ePO 5.0 servers installed with valid license key stop sending policies and tasks after 90 days