The Account with this error is on a Zimbra ZCS NEP 6.0.7 Server and in the Zimbra Webclient everything is working fine.

This message appears every minute or so and I have no Idea what the cause could be. So any help is appreciated. Thanks!

Code:
Product name:    Zimbra Desktop
Product version: 2.0
Build ID:        10580
Release type:    GA
OS Platform:     Mac OS X i386 10.6.4
Time of event:   2010-11-23 09:02:22
Error type:      mail.ALREADY_EXISTS
Item ID:         1073742689
Error summary:   message sync failed

Failure details - PLEASE REMOVE ANY SENSITIVE INFORMATION
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com.zimbra.cs.mailbox.MailServiceException: object with that id already exists: 1073742690
ExceptionId:sync-mbox-xxxxxxx@xxxxxxxxx.net:1290499342881:04dd83da82189350
Code:mail.ALREADY_EXISTS ArgitemId, IID, "1073742690")
        at com.zimbra.cs.mailbox.MailServiceException.ALREADY_EXISTS(MailServiceException.java:391)
        at com.zimbra.cs.db.DbMailItem.create(DbMailItem.java:191)
        at com.zimbra.cs.mailbox.Conversation.create(Conversation.java:239)
        at com.zimbra.cs.mailbox.Mailbox.createConversation(Mailbox.java:4733)
        at com.zimbra.cs.mailbox.ZcsMailbox.setConversationId(ZcsMailbox.java:345)
        at com.zimbra.cs.mailbox.DeltaSync.syncMessage(DeltaSync.java:804)
        at com.zimbra.cs.mailbox.InitialSync.saveMessage(InitialSync.java:1272)
        at com.zimbra.cs.mailbox.InitialSync.syncMessagesAsTgz(InitialSync.java:1027)
        at com.zimbra.cs.mailbox.InitialSync.syncMessages(InitialSync.java:960)
        at com.zimbra.cs.mailbox.InitialSync.syncMessagelikeItems(InitialSync.java:441)
        at com.zimbra.cs.mailbox.DeltaSync.deltaSync(DeltaSync.java:247)
        at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.java:89)
        at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.java:73)
        at com.zimbra.cs.mailbox.MailboxSync.sync(MailboxSync.java:178)
        at com.zimbra.cs.mailbox.ZcsMailbox.sync(ZcsMailbox.java:119)
        at com.zimbra.cs.mailbox.ZcsMailbox.syncOnTimer(ZcsMailbox.java:100)
        at com.zimbra.cs.mailbox.SyncMailbox$1.run(SyncMailbox.java:262)
        at java.util.TimerThread.mainLoop(Timer.java:512)
        at java.util.TimerThread.run(Timer.java:462)
Caused by: java.sql.SQLException: [SQLITE_CONSTRAINT]  Abort due to constraint violation (column id is not unique)
        at org.sqlite.DB.newSQLException(DB.java:374)
        at org.sqlite.DB.newSQLException(DB.java:378)
        at org.sqlite.DB.execute(DB.java:333)
        at org.sqlite.DB.executeUpdate(DB.java:354)
        at org.sqlite.PrepStmt.executeUpdate(PrepStmt.java:91)
        at com.zimbra.cs.db.DebugPreparedStatement.executeUpdate(DebugPreparedStatement.java:173)
        at org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:102)
        at com.zimbra.cs.db.DbMailItem.create(DbMailItem.java:179)
        ... 17 more