If you have two switches, and haven't done this already, down the administrative link between them:
From the CMM GUI, choose System | Switches | Advanced Configuration
Mouse over any port and choose Port Configuration
Select Port | 10G.XC | Admin Status | Down
and Port | 10G.SC | Admin Status | Down
If you only have one switch, then either you're getting some bad STP traffic, or the switch might be going bad. Can you check the Event Log for the switch, and see if there are occurrences of STP stopping ports from transmitting?