I got this working....
Go to the following locations... (in my case)
1) /opt/metasploit/apps/pro/msf3/modules/post/windows/gather/credentials/
2) /opt/metasploit/msf3/modules/post/windows/gather/credentials/
There you will find this "outlook.rb" and its leftover files like "outlook.rb.r15730" "outlook.rb.r16024"
Next delete all the above files.
And now run msfupdate , this will update the missing "outlook.rb"
hope this will help you .



