error in using metasploit

exploit= windows/smb/ms08_067_netapi
payload= windows/meterpreter/reverse_tcp

started reverse handler
exploit failed: login failed: smb server didi not replay to our request
exploit completed, but no session was created

how to solve it

another problem

started reverse handler
automatically detecting the target...
fingerprint: unknown - lang: unknown
no matching target
exploit completed, but no session was created.

i was specific the target but not solve this problem
anyone can help me...i'm using windows 7 ultimate
and backtrack 4 beta in vm