Open Transaction that won't go away SPID Ns There is a transaction that has been open on this instance since it was restarted and is preventing us from clearing the ldf. 

Here is the transaction information:

Transaction information for database 'MYDATABASE'.

Oldest active transaction:
    SPID (server process ID): 7s
    UID (user ID) : -1
    Name          : user_transaction
    LSN           : (54883:155655:1)
    Start time    : Jun 30 2014  5:45:35:820PM
    SID           : 0x01
DBCC execution completed. If DBCC printed error messages, contact your system administrator.


Does anyone know what 7s means, I have not yet seen a SPID with a letter in it. 

Thanks,
Craig

Update 14:03

I ran the resolution suggested here and this is the result after restart:

2014-07-18 14:01:12.83 spid7s      Mise à niveau des paramètres d'abonnement et des objets système dans la base de données [MYDATABASE].
2014-07-18 14:01:13.03 spid7s      Nom d'objet 'MSreplication_subscriptions' non valide.
2014-07-18 14:01:13.03 spid7s      Error executing sp_vupgrade_replication.
2014-07-18 14:01:13.03 spid7s      Saving upgrade script status to 'SOFTWARE\Microsoft\MSSQLServer\Replication\Setup'.
2014-07-18 14:01:13.04 spid7s      Saved upgrade script status successfully.


I still have the same problem. Any ideas on how to resolve this? 

Update 19/07
Problem solved by adding the  MSReplications_subscriptions table to the database where sp_vupgrade_replication was failing
I guess this is a known issue and Microsoft has released information about it in below links

Cause:

This issue occurs because the "tran_sp_MScreate_peer_tables" transaction was left open by a replication upgrade script during the upgrade. This open transaction prevents usual log truncation. 

Transaction log for database is growing with system SPID as open transaction

There is also a documented support article which will help you in understanding the issue

Database transaction log continues to grow after upgrade