Cisco Router Problem

I'm having a problem on a 2620. I can't get it to accept a sub interface on serial zero. I'm in global config and when I type "int s0.1" it says it's an unrecognized command. I can configure the normal serial interface with "int s0" but it doesn't like the subinterface command. It's IOS 12 - is there something I missing here?

nope, your syntax is correct. paste a 'show ver' and 'show ip int frief' here and let me look at it. Or for faster help. email it to me.

Thanks for offering your help - I forgot to check this thread. Turns out this guy copied IOS 11x from the tftp and it didn't jive with this router. It wouldn't accept encap fr either.