Put a pc on it if you want to use probably the quickest way if you want to use it, usually you go through another MGMT switch and through a firewall to process it
As I said though its not an error its a boot notification which can be ignored as your not using the port
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_55_se/configuration/guide/3750xscg/swint.html#pgfId-1730622
Understanding the Ethernet Management Port
The Ethernet management port, also referred to as the Fa0 or fastethernet0 port , is a Layer 3 host port to which you can connect a PC. You can use the Ethernet management port instead of the switch console port for network management. When managing a switch stack, connect the PC to the Ethernet management port on a Catalyst 3750-X or Catalyst 3750-E stack member.
When connecting a PC to the Ethernet management port, you must assign an IP address.
For a Catalyst 3560-X switch or a standalone Catalyst 3750-X switch, connect the Ethernet management port to the PC as shown in Figure 13-2.
Figure 13-2 Connecting a Switch to a PC
In a stack with only Catalyst 3750-X or Catalyst 3750-E switches, all the Ethernet management ports on the stack members are connected to a hub to which the PC is connected. The active link is from the Ethernet management port on the stack master through the hub, to the PC. If the stack master fails and a new stack master is elected, the active link is now from the Ethernet management port on the new stack master to the PC. See Figure 13-3.
In a mixed switch stack with Catalyst 3750 switches, only the Catalyst 3750-E and Catalyst 3750- X stack members are connected to the PC through the Ethernet management ports. The active link is from the stack master, a Catalyst 3750-E or Catalyst 3750- X switch to the PC. If the stack master fails and the elected stack master is not a Catalyst 3750-E or Catalyst 3750- X switch (switch 2), the active link can be from a stack member to the PC.
