Hi,
What is the threshold of that alert?
Please try to use get-queue |fl to check the queues on hub server.
Also you can use Queue Viewer to check that.
Do you have any related error information from event log? Please post the detail error event information here.
Also I recommend you to run ExBPA to check the Exchange status and then post the error information here.
By the way, how many Exchange Servers in your network? What is the version of your Exchange Server and SCOM?
If you have event 2115 in event log, then please try to restart the health services and check the issue again.
If you find any agent is in grayed out status, then please try to restart and monitor the issue.
SCOM 2007,Alert generated by Send Queue % Used Threshold
http://blogs.technet.com/b/csstwplatform/archive/2010/09/21/scom-2007-alert-generated-by-send-queue-used-threshold.aspx
Xiu Zhang
TechNet Community Support
