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Cause:
This is a known Jira issue - check this Atlassian KB article https://confluence.atlassian.com/jirakb/ora-00955-name-is-already-used-by-an-existing-object-144212317.html
Resolution:
Following the steps in Resolution for Cause #2 from the KB article should resolve this. If not - reinstall Configuration Manager for JIra following these steps:
1. Uninstall CMJ (https://appfire.atlassian.net/wiki/display/CMJ/Uninstallation)
2. Stop JIRA
3. Drop all CMJ AO_3A112F tables
4. Drop all CMJ AO_3A112F sequences
5. Start JIRA
6. Install CMJ