PowerConnect 3348 / Cisco 3750 trunking issue?

I am having a problem trunking the 3348 and 3750. I have two 3750's that are stacked together as one and one 3348.

On the 3348, I am using 1/g1 and 1/g2 to trunk to g1/0/1 and g2/0/1 of the 3750 respectively.

Here's the issue:

If I only use either one of the trunking ports, there is no problem. It is when I try to plug in the other port, I start losing connections. I have users on other switches that are connected to the 3750 that are not trunked. Users start losing connection to the network when I have both of the trunks plugged in on the 3348 and 3750.

Here's the configuration for the 3348:

dell-3348# show run
port storm-control enable unknown fastethernet
port storm-control enable broadcast fastethernet
port storm-control enable multicast fastethernet
interface port-channel 1
spanning-tree portfast
spanning-tree cost 4
exit
interface range ethernet 1/g(1-2)
speed 1000
exit
interface range ethernet 1/g(1-2)
switchport mode trunk
exit
vlan database
vlan 100
exit
interface range ethernet 1/e(1,47)
switchport access vlan 100
exit
interface range ethernet 1/g(1-2)
switchport trunk allowed vlan add 100
exit
interface vlan 100
ip address 192.168.1.2 255.255.255.0
exit
interface vlan 1
ip address 192.168.5.5 255.255.255.0
exit
hostname dell-3348

Here's the configuration for the 3750:

spanning-tree mode pvst
spanning-tree extend system-id
!
!
interface GigabitEthernet1/0/1
description Dell-3348 trunk 1/g1
switchport access vlan 100
switchport trunk encapsulation dot1q
no ip address
speed 1000

.....

interface GigabitEthernet2/0/1
description Dell-3348 trunk 2/g1
switchport access vlan 100
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 1000

Kien