Hi there, the management port can be used only from software version 12.2(46)SG and later.
See the New Software Features in Release 12.2(46)SG here:
http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/release/note/OL_9592.html#wp820800
If you have a software release earlier than 12.2(46)SG, management port can be used only from ROMMON.
Hope this helps.
Best regards,
Andras