Alert on a No Messages In a Queue

Hi

I have A SCOM 2012 Server that is monitoring 3 2012 servers that are outside of my organization.

All 3 sever are not members of our Domain and are connected to the SCOM sever.

I can monitor services, Queues , CPU ,Disks etc. 

I am trying to create a monitor on a private error queue. I can see the no of messages in the queue in queue performance view.

I want to create a monitor/Alert that will be activated when the no of messages in this queue will be greater then the requested threshold.  

I have created a monitor with Object "MSMQ Queue" , Counter : "Messages in Queue" and
Instance "[server name]\private$\error"

I have set the threshold to 1 , defined the alerting option.
I have 300 messages in the queue and the no is going up but no alerts are sent.

I do not  know why there are no alters.

Thanks

Itamar

Itamar