Ports silently going to disable mode

[nawas]

I have this Cisco 6509 running 12.2.18SXF7b and it has Sup32 and WS-X6248 and 6348 line card. I have started noticing this strange behavior I see that several ports go into "disabled" mode. These are not only the uplink ports but also the ports where I have PC and thin client connected. all I see in the logs that port went down and then I have to go in and manually enabls the port. I have udld aggressive enabled, I removed aggressive but no help. My uplinks are LACP port channel to another 6500 with sup720 running 12.2.33SXJ1.
My access port config is

switchport
switchport access vlan xx
switchport mode access
switchport nonegotiate
switchport voice vlan YYY
no ip address
speed 100
duplex full
spanning-tree portfast
spanning-tree bpduguard enable

[glen.grant]

It should say something in the logs as to why the switch is putting the ports into err-disable .

[nawas]

After enabling more monitoring I found out that it could be NAC but not sure yet. This version of IOS does not support

snmp trap mac-notification therofore NAC is  using link down/up trap to move hosts from Dirty Vlan to Clean Vlan but i still do not understand why NAC would be shutting the port down. Cisco TAC thinks it is NAC, but not certain yet. Anyone have an idea?

[Leo Laohoo]

try the command "sh interface status err".