errdisable_recovery.pdf explains why our HP-Blade suddenly has disabled port (turn red light from initial green) when connected to a switch.

This blade Catalyst 3020 ports must have been in errdisable/error disable state. First, look for something like

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#show interfaces gigabitethernet 4/1 status
 
Port    Name       Status       Vlan       Duplex  Speed Type
Gi4/1              err-disabled 100          full   1000 1000BaseSX