ramachandraraju,
I was actually able to simulate your issue the other day. I have RRAS setup on one of my servers and I attempted to VPN in from an external Internet connection and I actually got the same error. Unfortunately, the issue was intermittent because when I retried on my XP machine and a Vista machine I had with me I was able to connect without issues multiple times.
I currently don't have my home router setup with the PPTP passthrough option enabled so this is probably why it occurred.
