After installing JIRA 2.5.2 I added an issue and got an ConnectionException + InternalWorkflowException.

[FATAL] XMLWorkflowFactory - -Error creating workflow descriptor
<java.net.ConnectException: Connection timed out: connect>
2003-11-26 17:24:58,331 ERROR [web.action.issue.CreateIssueDetails]
com.opensymphony.workflow.InternalWorkflowException
java.net.SocketException: Connection reset by peer: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
....

The reason is that our bugtrack server is behind a firewall and could not connect to zeus.atlassian.com to download
the /osworkflow/workflow_2_5.dtd file (which obviously is needed).

This is not documented, and i can't find an option to let JIRA go over our proxy. I had to open our firewall for zeus.atlassian.com.

This should be at least stated in the requirements for JIRA, the file should be shipped with the standard install, or an better errormessage should be generated, because it prevents adding new issues and leaves one pretty puzzled.