Log Name: Application
Source: Microsoft-SharePoint Products-SharePoint Portal Server
Date: <Todays Date>
Event ID: 5553
Task Category: User Profiles
Computer: <SharePoint Server Name>
failure trying to synch site <Site GUID> for ContentDB <Content Database GUID> WebApp <Web Application GUID>. Exception message was Cannot insert duplicate key row in object 'dbo.UserMemberships' with unique index 'CX_UserMemberships_RecordId_MemberGroupId_SID'.
The statement has been terminated.
stsadm -o sync -listolddatabases n
stsadm -o sync -deleteolddatabases n
where 'n' is the number of days that have passed since the databases have been synchronized
The '-listolddatabases' command lists the content databases that have not been synchronized since 'n' days while the 'deleteolddatabases' command performs the same operation as the listolddatabases parameter, except it deletes old records corresponding to these databases. It does not delete the databases themselves. Once the synchronization references are deleted and a new profile synchronization occurs, new references will be stored in the database.
You must run the stsadm shell as the farm account for the previous commands to work successfully.