The reported error is from the Allegro/Presto/Vivace version of the Server, which supports trial (i.e. evaluation) licenses.
Expired trial licenses can be restored by asking info@lightstreamer.com (as you did).

If you have downloaded a license file for the free Moderato version, note that you also have to download the software package for the Moderato version and follow the instructions in the included GETTING_STARTED.TXT to make it work.