I guess the switch either doesn't provide VLAN information in its SNMP tables, or it does so in a way the Port Mapper doesn't understand (we support two locations: vmMembershipEntry and dot1qVlanCurrentEntry).
If you could run the
snmpwalk tool against your switch,
open a support ticket and attach the snmpwalk's output, we may be able to see what happens there and advise further.
We have also ordered the switch, to run some of our tests as well.