How exactly do you have your computers setup - are your using a wireless router, switch/hub to share the internet connection ?

Having the Same IP addess is not a good idea - as you will see conflict Ip messages and also have interrupted sessions - as the wrong host resolves its MAC address to the SAME Ip address.....not a good idea. I would recommend increment one of the PC's host IP address by one, i.e 192.168.0.1 and 192.168.0.2....as pure examples

To your specific error message - check out following URL.
Microsoft Knowledge Base Article – 168720
ERROR Message TCP/IP CP Server the on Available Not Is Protocol Network This for Control PPP 733: Error Reported :

<http://support.microsoft.com/default.aspx?scid=kb;en-us;168720>

I have 2 computers set up 4 hours apart.  Both are on cable modems connected all the time.  I thought I was setting it up right with both systems set up with incoming connections and each was setup to connect to the other one with outgoing connection.  I set up each one to accept virtual private netoworking.  I also set up a login and password for each computer so I would be able to log in.  I have them both firewalled (not sure if that was the problem)  But when I went to connect them I was unable and recieved the error.  I had the right IP address also for both systems.  I would love to find a step by step or even write one after I figure this out.  Not sure how many VPN's are out there in use.  Would love any comments.  Thanks.

The only commercial VPN server I've set up is Checkpoint. It needs UDP/500 (ISAKMP) and IP/50 (ESP) let in and out. I don't know whether the XP firewall deals with any IP packet types other than TCP and UDP, though.

Jim

Okay now I see that you're trying to create an IPSEC tunnel through the Internet between two separate sites - this was not clear before. The fact that you mentioned the IP addresses are the same - means you must be running in NAT (network address translated mode).

How have you setup your filter lists and IPSEC policies - as these need to match exactly if a peer-peer IPSEC session is to be established and correct negotiation of SA (Secuirty Associations) achieved ?

What IPSEC mode are you using  (Tunnel orTransport) ?

Since you are trying to achieve an end-end IPSEC session, then you should be in Transport mode, as no intervening router is being used to encrypt/decrypt the traffic.........unless you have configured a router to do this for you ?

Note : Also be aware that an IPSEC frame adds 40 bytes to the size of a L2 frame - so a maximum sized ethernet frame would become 1540 bytes........which is invalid - therefore when using VPN/IPSEC tunnels you should tune your maximum MTU to 1400 bytes.

Each IP address for the two computers is different.  That is not a conflict.  I have them both set up the same but I will look at the IPSEC situation and see how it is configured.  On the netork connections for both of the computers I set them up to allow incoming connections with both VPN settings and I am going to add the IP security one in the properties.  It must be something with the way I have the settings setup.  I have another computer closer to one of them and I am going to try and connect that way before heading up the other one.