You must have the exact same credentials on both computers. ex: Your username and password that you use to log in on one PC has to be exactly the same as it is on the other.
Also, I'm assuming that you have set both computers to allow remote access both to and from?.?.? And right under where you type in the IP address of the PC you wish to connect to(remote PC), it should have you trying to connect as *remote PC name*\*username*. (if you have not named the PCs on your network, you need to do this) right-click on "my computer" and go to properties, scroll down to where it says your computer names. It's easier if you make all the names the same. Also make sure you have both PCs on the same workgroup, if this is a home network, just name the workgroup "workgroup". if not, name it whatever just so long as it's the same on all PCs you wish to remote to. Try these things and let us know!
Dr.Bowers