Here is the hardware limitation description to MHSRP. I don't believe that the 2600 is affected, but do a show int to check:
"Ethernet Several Ethernet (Lance and QUICC) controllers in low-end products can only have a single unicast MAC address in their address filter. On these platforms only a single HSRP group is permitted, and the interface address is changed to the HSRP virtual MAC address when the group becomes Active. If you're using HSRP on routers with multiple interfaces of this type, you should configure each interface with a different HSRP group number. "
The key here is the ethernet controller "Lance".
router#show interface ethernet 0
Ethernet0 is up, line protocol is up
Hardware is Lance, address is 0010.7b36.1be8 (bia 0010.7b36.1be8)
Internet address is 10.200.40.74/22
http://www.cisco.com/warp/public/619/hsrpguide5.shtml
Mick.
