Failed to flush the commit table to disk in dbid 5 due to error 2601

I have a database with Change tracking enabled and when i tried to backup i got this error:
Failed to flush the commit table to disk in dbid 5 due to error 2601. Check the errorlog for more information. (Microsoft SQL Server, Error: 3999)

I read the posts related to this topic but i still can get it to work. Turn off and on Change tracking will make me reinitialize all the mobile devices that synchronize with this database.
Also updated SQL Server 2008 R2 SP2 with CU4 but i'm still getting the error.

Help anyone ?

Thanks in advance.