Symptoms

Synchronization fails and the following appears in atlassian-confluence.log:

2013-10-14 13:13:56,551 ERROR [scheduler_Worker-3] [atlassian.crowd.directory.DbCachingDirectoryPoller] pollChanges Error occurred while refreshing the cache for directory [ 622595 ].
java.lang.IllegalStateException: Unable to rename user x to X

Cause

Username case in the cwd_user table is different than the one stored in LDAP.

Workaround 1

Disable incremental synchronization for this user directory and re-run the full synchronization. You can expect it to be completed successfully.

Workaround 2

If workaround 1 fails, please run the following SQL query to manually update the offending entry:

UPDATE cwd_user set user_name='X' WHERE user_name='x' AND directory_id != (SELECT id FROM cwd_directory WHERE directory_name='Confluence Internal Directory');
UPDATE user_mapping set username='X' WHERE username='x'; 

After that synchronize your user directory and it should complete successfully.