3Com Switch 4800G 24-Port - Page 1179

Troubleshooting Port Security 1179
Solution
Use the cut command to forcibly disconnect the user from the port before
changing the port security mode.
[Switch-GigabitEthernet1/0/1] cut connection interface gigabitethernet 1/0/1
[Switch-GigabitEthernet1/0/1] undo port-security port-mode