A Jira deployment is failing. The web services are listening on port 8080 or whichever port you configured. But the web UI does not load. What should you do?
Root cause: "...JIRA is not designed to import data from a new version into an older version." taken from Atlassian's website.
Has the database been used in the past? If you downgraded your Jira instance, the database needs to be empty or restored from a backup. Once Jira has been upgraded and connected to a SQL database, that database will not work for older versions of Jira.