I am trying to rename a user from upper case to lower case using rename users pl

I am trying to rename a user from upper case to lower case using rename users plugin and facing the following error. Please help.

015-03-03 19:11:20,683 GMT INFO [stdout] (default-threads - 14) at org.jboss.threads.JBossThread.run(JBossThread.java:122)
2015-03-03 19:11:20,683 GMT INFO [stdout] (default-threads - 14) Caused by: com.appiancorp.suiteapi.common.exceptions.DuplicateNameException: com.appiancorp.suiteapi.common.exceptions.DuplicateNameException: Duplicate names are not permitted
2015-03-03 19:11:20,683 GMT INFO [stdout] (default-threads - 14) at com.appiancorp.a2.plugins.userServices.RenameUserService.updateUsernames(RenameUserService.java:148)
2015-03-03 19:11:20,683 GMT INFO [stdout] (default-threads - 14) at com.appiancorp.a2.plugins.userServices.RenameUser.run(RenameUser.java:93)
2015-03-03 19:11:20,683 GMT INFO [stdout] (default-threads - 14) ... 66 more
2015-03-03 19:11:20,684 GMT INFO [stdout] (default-threads - 14) Caused by: ...

OriginalPostID-140312

OriginalPostID-140312