ESP problem with MS RRAS to Cisco 3000 VPN passing through PIX 515E Firewall.

Hello,

I'm having a problem creating a MS RRAS server to a Cisco 3000 VPN
concentrator passing through a PIX 515E Firewall (6.1). The
configuration is as follows. The MS RRAS server has a configure IPSEC
policy creating a tunnel withe the external interface of the PIX
firewall. The PIX firewall passes that traffic to one of its internal
interface connected to the VPN concentrator. There is a sepearate
internal interface connecting to the internal LAN for internet
connectivity. UDP 500 is static translated to the VPN concentrator.
UDP 10000 is also static translated to the VPN concentrator. I am able
to estrablish the tunnel but if I try to pass traffic through it I get
"Regular Translation Creation failed for IP protocol 50" on the PIX.
Obviously this results from the fact that I can't static IP protocol
50. If I try to connect with the Cisco client from the outside it
works because it is encapsulating ESP in UDP 10000. Is there a way to
make the RRAS server do this? If I can't get RRAS to work this way
it's not a big deal because I can use L2TP but I will have other VPN
concentrators connecting through the PIX from the outside. Will they
have the same problem or will they encapsulate ESP in UDP 10000?
Any suggestions or thoughts would be greatly appreciated.

Thanks,
Sean