Duplicate constraint violation due to duplicate hibernate users when migrating them to Crowd directory

2011-04-13 14:48:38,854 WARN [main] [confluence.user.migration.AtlassianUserDataMigrator] processRowInternal Duplicate entries found for user name 'nbhawnani', which probably means there were two user names which only differed by case. The first entry found was used, so this user's password and details may not be correct.
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2011-04-13 14:48:41,416 ERROR [main] [sf.hibernate.util.JDBCExceptionReporter] logExceptions ORA-00001: unique constraint (CFLUENCE.CWD_UNIQUE_MEMBERSHIP) violated

2011-04-13 14:48:41,417 ERROR [main] [sf.hibernate.impl.SessionImpl] execute Could not synchronize database state with session
2011-04-13 14:48:41,678 ERROR [main] [atlassian.confluence.upgrade.UpgradeLauncherServletContextListener] contextInitialized Upgrade failed, application will not start: java.lang.RuntimeException: net.sf.hibernate.exception.ConstraintViolationException: could not insert: com.atlassian.crowd.embedded.hibernate2.HibernateMembership#23332935
com.atlassian.confluence.upgrade.UpgradeException: java.lang.RuntimeException: net.sf.hibernate.exception.ConstraintViolationException: could not insert: com.atlassian.crowd.embedded.hibernate2.HibernateMembership#23332935
at com.atlassian.confluence.upgrade.AbstractUpgradeManager.upgrade(AbstractUpgradeManager.java:109)
at com.atlassian.confluence.upgrade.impl.DefaultUpgradeManager.upgrade(DefaultUpgradeManager.java:139)
at com.atlassian.confluence.upgrade.UpgradeLauncherServletContextListener.contextInitialized(UpgradeLauncherServletContextListener.java:28)
at org.mortbay.jetty.handler.ContextHandler.startContext(ContextHandler.java:548)
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Caused by: java.lang.RuntimeException: net.sf.hibernate.exception.ConstraintViolationException: could not insert: com.atlassian.crowd.embedded.hibernate2.HibernateMembership#23332935
at com.atlassian.confluence.upgrade.upgradetask.SessionClearingRowCallbackHandler.flushAndClear(SessionClearingRowCallbackHandler.java:54)
at com.atlassian.confluence.upgrade.upgradetask.SessionClearingRowCallbackHandler.processRow(SessionClearingRowCallbackHandler.java:41)
at org.springframework.jdbc.core.JdbcTemplate$RowCallbackHandlerResultSetExtractor.extractData(JdbcTemplate.java:1248)
at org.springframework.jdbc.core.JdbcTemplate$1QueryStatementCallback.doInStatement(JdbcTemplate.java:395)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:343)
at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:405)
at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:409)
at com.atlassian.confluence.user.migration.AtlassianUserDataMigrator.migrateGroupMemberships(AtlassianUserDataMigrator.java:176)
at com.atlassian.confluence.upgrade.upgradetask.AtlassianUserToEmbeddedCrowdDataUpgradeTask.doUpgrade(AtlassianUserToEmbeddedCrowdDataUpgradeTask.java:74)
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select name, count(name) from users group by name having count(name) > 1;

select u.name, u.id, p.date_val as lastLogin from users u
join OS_PROPERTYENTRY p on u.id = p.entity_ID
where entity_key='confluence.user.last.login.date' AND u.name='yourDuplicateUserName'
order by date_val desc;

delete from local_members where userid = xxx;
delete from users where id = xxx;