It is possible that after the firmware update the auto-negotiation on the ports is not compatible.  Do you have both sides set to dynamic/auto?  I see the 3COM lag is dynamic.  You may try setting the speed manually.  If no change try these steps to verify the hardware functionality. 1)Disable and restart the problematic port on the Dell switch. From the command line the command will look similar to: config #interface ethernet 1/xg1 #shut #no shut 2)Loop back the fiber cable to another available port in the PC6224F switch. Example: if the problematic port is 1, loopback the same cable coming from port 1 to port 2 or any other available port on the same switch to see if port 1 link light comes up. If they get link light to come up this is an indication that both ports are OK, both fiber optical transceivers are OK and that particular optical cable is OK. That, more likely, will confirm an auto-negotiation issue within the Dell 6224F and the 3COM switch.
Recently we have upgraded our Dell Powerconnect 6248's from 2.x.x to 3.2 and 3.3.x versions of the firmware. We have tried using a non-dell SFP SX optic, and a Dell brand new SFP SX optic in both versions. Under 2.x.x the SFP's both work fine and we're able to pass traffic with no issue.After upgrading to 3.2.x and 3.3.x we no longer receive a link light on the SFP's.  I can't find any specific setting that we need to change or anything like that. Is there something we're missing? We really need to upgrade as we have a stack on 2.x.x that we are unable to save the config on: when we run copy running-config startup-config it fails to save to the stack, so everytime we reboot the switch we have to re-configure the settings. I can't find any mention of either issue.  Any help would be appreciated. -Mike
Powerconnect 6248 SFP Not working after upgrade to 3.2.x and 3.3.x (Also copy 
running-config startup-config failures on 2.x.x).