You may experience the following error if you copy your existing license key to another server, which mismatches each other.
[WARNING] Server signature does not match the license key #2. Please request a new license key! 2018-03-28 19:59:36.226011 [NOTICE] Memory size is: 16270292KB. 2018-03-28 19:59:36.621328 [ERROR] [LICENSE] License key operation failure: EXCEPTION LCA.2: fail to process
In another case, from LSWS admin, in the version manager, you may see Web Host Essential though you have a Web Host Professional license, which mismatches each other too.
In this case, you should re-register a new license key for your server. Please run the following from command line.
/usr/local/lsws/bin/lshttpd -r /usr/local/lsws/bin/lshttpd -V /usr/local/lsws/bin/lswsctrl restart