Question about MetroSync Manager Block device support

Folks,

Being busy with the implementation of a UNITY XT storage array, I'm a bit confused about MetroSync replication, in particular the witness software, MetroSync Manager and I'd need some help.

My setup consists in two arrays, FC connected.  I have a couple of block device provisioned, synchronously replicated, everything fine, everyone is happy.  However, I've read about MetroSync Manager, which, I thought, could help us and take care of failover in case of any unplanned event, for that reason I installed the software on a third site, as a tiebreaker.

After software installation and configuration, it has no problem to detect my arrays, but refuses to start the service, logs are saying:

"no session found on site xx.xx.xx.xx"

Since I cannot find any relevant document clearly saying block devices are not supported with MetroSync Manager, I'm still believing something must be incorrect in my configuration but starting to give up and thinking this feature is limited to file...

Does anybody have a similar experience ? can help or provide me some more information ? 

Thx 

Marvin