An essential clue in trouble shooting are log files. Our Communardo Support asks in some cases for the JIRA log.
If you have not changed the destination of the log files in your JIRA, you can find your log at your JIRA server:
<Jira Home Directory>/log/atlassian-jira.log
If you don't know where your JIRA Home Directory is located, you can look it up in your JIRA Administration -> System Information. There you can find an entry called "Location of JIRA Local Home".
Please note, that log files can be very large. If you attach the file to your support ticket, it must not be larger than 10 MB.