I need help getting a PPTP connection through a firewall

We run a SonicWall Pro2040.  I'm trying to get a mobile device to establish a PPTP connection to a Windows 2003 PPTP server so I can run some remote Administration from my mobile Unit (Treo 650).  I have MergicVPN installed on the Treo.  I've enabled RAS on one of my W2k3 servers, added to the RAS servers group, and enabled PPTP.  On My Sonicwall, I've added a NAT policy to point to the internal PPTP server, and when I try and connect, the Treo appears to get to the server, and then I get a "Error: Account does not have VPN permission".  I don't know if this is an issue on the SonicWall or on my PPTP server....I always VPN to the firewall from my laptop using IpSec, but this PPTP stuff is all new to me.  I only need to configure myself to use a PPTP connection, that's it.  Thanks.