Hi Marc,
HSRP is an L3 function, so we need to know the L3 configuration in order to solve this problem.
I assume you have trunks between the 4510 and each 6500. The link between both 6500s DOES NOT CARRY VLANs 31 and 43, right?
If they do, the HSRP-interfaces still 'see' each other when one link to the 4510 goes down, and HSRP will not awitchover.
On both standby routers, you need an interface in both VLANs (int vlan 43 and int vlan 31 resp).
Next test: can you ping each physical IP-address from both vlans?
Next test: can you ping the virtual IP address?
What is the output of 'show standby'?
With the router-configs I can be more specific.
Groet,
Marcel
