If you get a -15,3002 Can't connect to License Server error, it's more than likely that the server has a conflict with another license program on the machine. I've seen this occur frequently with eCognition, but other software cause the issue as well.
The only way round it is to uninstall the other license servers or software and then restart the ERDAS license server from Services. That, or use another machine as a license server.
It's also possible that there is an issue with security settings / firewall. See related article.