From the secondary/standby unit can u ping itself? It responds correct?
From the active unit you are unable to ping the standby IP.
From the standby unit are you able to ping the active IP?
Does the swich show both the mac address in the CAM table for the VLAN?
If upgrading is the only thing that changed to break this, I'd suggest opening a TAC case to investigate this further.
-Kureli