See @Gary post below from the following thread
https://forum.emclient.com/t/licenseserver-cant-be-reached-since-last-10-days/80922/4
(Gary’s post)
“eM Client needs to periodically contact the license server to validate your license. If you have a firewall or VPN that is blocking the connection, then eM Client will eventually be disabled”.
“Can you see if these links open in your web browser”:
https://licensing.emclient.com
https://licensemanager.emclient.com
http://emclient.com
“No need to login on the pages, just open them”.
“If they don’t open you will need to configure those VPN or firewall applications to allow access to those addresses, then restart eM Client”.
“If you can reach those web pages, but the license server still cannot be reached, then it may be that some apps turned off specific services that are required”.
“Click on the Windows Start button and type Services Open the Services option from the results”.
“Check that both Cryptographic services and CNG Key Isolation are running. If they aren’t, start them”.