Remote Login

My problem is I cannot login to a remote desktop. He give me the code but when I type them on my computer and connect it says ‘‘code could not be …’’ With my PC, I logged into other with no problem. When the other which I could not log into try to log in mine by entering the code, it’s working. He has 2 computer which I can’t log into. Mine has Win7 and his are XP and Win7. What’s going on? Thanks.