Yet another event ID 5553 error..

Hi all,

I noticed a lot of event ID 5553 errors on this site but I have tried almost all of it and it seems to not be solving the issue. Specifically the error I get is this:

failure trying to synch site 3d0b5889-cf98-4d4f-8212-f35d602f88e6 for ContentDB 14a09b1b-3984-4499-bf1d-c9e517911f8b WebApp a26f4ded-f07a-4e0f-8c70-e3f38dca95d7.  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..

My Sharepoint 2010 is running on 3 separate VMs as such:

1) Sharepoint server

2) SQL server

3) AD authentication

I have tried the following steps to try to fix this:

1) stsadm -o sync -listolddatabases 0

Result:

User Profile Application 'User Profile Service Application' - Partition '0c37852
b-34d0-418e-91c6-2ac25af4be5b'
ID: 14a09b1b-3984-4499-bf1d-c9e517911f8b  Synchronized: 1/4/2013 2:44:50 PM

stsadm -o sync -deleteolddatabases 0

Result:

A failure occurred during the processing of this command. Check diagnostic logs
for more information.

2) I have tried to delete the AD server connection by going to Central admin > Manage service apps > User Profile service application > Configure synchronization connections. Went to Monitoring > review job definitions > click on "User Profile Service Application - User Profile to SharePoint Full Synchronization" and click on run now. Same error occurs.

Anything else I should try? Any help greatly appreciated.