what kind of license file do you use? The free one which is available via this community? Or do you use an (evaluation) license which has been given to you by Software AG?
I am using a professional license (3 users) we bought from SAG.
Are you sure that the license file is used by one installation of MashZone, only? If not, it might be the trigger. Once MashZone servers detect an indentical key used by other servers they shut down each other.
MashZone's log files are found within your installation directory, i.e. within system/tomcat/logs.
In case your problem persists I may ask you to direct your question to ARIS support to troubleshoot offline.