Without further information I can only guess...
But did you configure the VLANs on the uplink ports to each of the 3com switches?
Let's say your switches were plugged into ports 44 through 50 and your 2 VLANs were 1 and 10. Then to tag them it would be.....
vlan 1
name "MY FIRST VLAN"
tagged 44-50
exit
vlan 10
name "my second VLAN"
tagged 44-50
exit