Wake on LAN / Magic Packet broadcast doesnt work through PPTP

Hi, I have a network, where I want to use WOL from a remote PC. It works when I send a packet from inside the network (or on the server).
If I connect via PPTP from a remote Windows XP PC, I can’t wake up the PC on the LAN. I suspect the broadcast packet doesn’t reach the LAN. The PPTP connection have IP 192.168.16.127/24, DNS + Wins 192.168.16.2, gtwy 192.168.16.127. I can ping and remote control the PC?s on the LAN.
Configuration: Internet, Router (Fixed IP), External NIC, Small business server 2000, Internal NIC.
Router (internal side) 192.168.1.1
External NIC 192.168.1.2/24, gtwy 192.168.1.1, DNS + Wins 192.168.16.2
Internal NIC 192.168.16.2/24 no default gtwy, DNS + Wins 192.168.16.2
Isa server Local Address Table 192.168.16.0 ? 255 (LAN) + 172.17.51.1 ? 172.17.51.4
No blocking packet filters
Everything works OK (except WOL via PPTP)
Any suggestions are welcome