As people test out Service Manager and the integration to Operations Manager, this question comes up pretty often.  The situation is typically that a connector has been created between SCSM and SCOM.  Then at some point SCSM is uninstalled and a new version of SCSM is installed.  The connector for SCSM remains in SCOM.  The alerts that match the criteria for the alert connector subscription will still be marked for forwarding to the old SCSM installation but will never be picked up.  So – in this case you have a couple of options:

1) Remove all of the subscriptions for the old connector.  This will prevent any alerts to be marked for forwarding to the old connector.  The alert connector will remain in this case but isn’t doing anything.

2) Delete the alert connector following the instructions you can find in this blog post on Kevin Holman’s blog:

http://blogs.technet.com/kevinholman/archive/2009/09/10/removing-an-old-product-connector.aspx