I started the Desktop version of the software, a server management screen is shown and I cannot connect to the server

Prior to Twin 2.1.0 and Explore 1.3.0 Omixon HLA software installers came in bundles. The desktop version of the software contained both a client executable and a desktop executable. If you have a desktop version, make sure that you have used the correct executable (e.g. omixon-hla-twin instead of omixon-hla-twin-client).