what are your configuration settings?
the command is
monitor session [id] source [interfaces] [both | rx | tx]
monitor session [id] destination [interface] [encapsulation] < for VLANed environments.
you have some restrictions for directions [RX | TX] in some IOS versions and platforms though.
if you send a little more info abt ur network and settings, you get better help.
Soroush.
Hope it Helps!
Soroush.
