We've installed two confluence at one windows web server as a service, (use 8090, 8092 port)
one MSSQL DB server with two category .
Each confluence started without problem.
but sometimes one confluence occured fatal error during live service :
Non Clustered Confluence: Database is being updated by another Confluence instance. Please see http://confluence.atlassian.com/x/mwiyCg for more details.
We restart service when this error occured, but it happens again.