Multiple port channel configuration

Hi,

I cant find the Force10 support forum, so i'll post my question here.

We have 2 Force10 S48's acting as a core, and 3 Cisco 2048's acting as an access layer. I have configured the switches as follows:

Cisco1 port 1234 - Force10 1 Port 1234

Cisco2 port 1234 - Force10 2 Port 1234

Cisco3 port 5678 - Force10 1 Port 5678

The strange thing is, I had to connect the first Force10 to the 3rd Cisco on port 5678 of the Cisco. When i connected it to port 1234, Cisco switch 1 or 3 would stop working - almost like STP blocked the port.

Now this suggests that the Force10 doesn't like sending traffic to port 1234 on different devices, which doesnt really make sense to me. Does anyone know why i cant use port 1234 on different devices that connect to the Force10?

Regards,

Jon