Hi Francisco,
I think it is due to typo. It is "ip spd mode aggressive" but you wrote "ip spd mode agressive" You need one more "g" letter.
I jsut check handly one and it is accepted.
3640(config)#do show ver | i image
System image file is "slot0:c3640-is-mz.123-3c"
3640(config)#do show ip spd
Current mode: init.
Queue min/max thresholds: 73/74, Headroom: 100, Extended Headroom: 10
IP normal queue: 0, priority queue: 0.
SPD special drop mode: none
3640(config)#ip spd mode aggressive
3640(config)#do show ip spd
Current mode: init.
Queue min/max thresholds: 73/74, Headroom: 100, Extended Headroom: 10
IP normal queue: 0, priority queue: 0.
SPD special drop mode: aggressively drop bad packets
3640(config)#
Regards,
Kimihito.