I have a Win7x64_SP1 Desktop, and a Win7x32_SP1 netbook. I installed the respective CPU appropriate versions of 188.8.131.52 on each of them. Both have static IPs behind the router.
When I try to connect from my desktop to my netbook via the IP address, it connects just fine, and then asks me the password, which is fine, but no matter what I type, it tells me Authentication Rejected. Just for the heck of it, I experimented and set the password on the netbook to "123" in the settings app, so that it would be simple, and then I tried using that, but it still rejected me. I also tried checking the "Password Required" box, (which BTW acts like it means "no password required") and it doesn't ask me for a password on connection, but then it still rejects my Authentication, which is odd in itself, because that shows that it's not working at all.
Then alternately, when I go the other way, and try to connect from my netbook to the desktop machine, it asks for a username and password, but the funny thing is that I can't remember ever setting any kind of username, and can't find any place for a username in the settings app, so therefore I don't know what it is expecting.