Ya why not google up on exploits, this isnt like cracking wep, its incredibly complex. There are so many things that could go wrong its pointless for me to even start listing them.
You might want to try it on a VM, or another pc on your local net before you attempt to infect your "friend" .. which i must say is highly suspicious in the first place.
Im not sure what your doing wrong but i can tell you it has nothing to do with metasploit, its most definitely user error. If you manage to fix that issue all should be ok