PPTP help please

Hi, I need some help with the following scenario

I have a routerOS 3.10 wireless cpe at my client site
I have a public ip on the wlan1 interface
I have a private ip on the ether1 interface with a src-nat rule masquarading the private ip range to the out interface(wlan1) which nat’s all internal traffic to the public ip on this interface - this all works fine.
I have setup a PPTP connection which provides an external XP pc with a VPN(PPTP) connection with a private IP from the internal range of the company.
The connection seems to register the pc onto the network and I can ping as far as the ether1 interface of the router BUT I cannot ping any other lan devices

Am I missing anything obvious?

cheers

Rob

ARP=proxy-arp should be enabled on the local network interface, if PPTP client uses the same IP addresses as on local network interface.