You need an IPSEC SPA to do encryption on the Catalyst 6500 switches.
Without a SPA-IPSEC-2G or IPsec VPN Acceleration Services Module, the IPsec Network Security feature (configured with the crypto ipsec command) is supported in software only for administrative connections to Catalyst 6500 series switches and Cisco 7600 series routers.
Please refer the below URL for details:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/122sx/ol_4164.htm#wp2565092
I hope it helps.
Regards,
Arul