PPTP connections being blocked

Archived from groups: comp.dcom.vpn,comp.dcom.sys.cisco (More info?)

I've got a Cisco 3005 VPN concentrator that I'm trying to set up for
PPTP connections. I'm pretty sure that PPTP is enabled, and that it's
available as one of the protocols for all groups. And it's being
allowed through the public filter on the public interface. But when
trying to connect, I get "no answer" errors. Is there any other
possibility for me to check other than there might be packet filtering
going on somewhere upstream?

Thanks!