I click on someone in a email and am trying to respond to them, a new box for MS outlook appears?

I use to be able to respond to emails and email names on my yahoo messenger list but now I get a strange box that says MS Outlook and tries to launch pop3's and all sorts of stuff? Anyone?
I click on someone in a email and am trying to respond to them, a new box for MS outlook appears?
ok...well...MS Outlook is basically an email/file sending program much like yahoo and a lot of times is set to default on one's computer. So...sometimes when you click on someone's email adddress/name the program thinks you are trying to send them an email so it opens a new window with this program. This is a program that many people have on their computers but do not use since there are sites such as yahoo and hotmail that do the same thing for free. Basically if you want to send an email to someone just open up your yahoo account and do it thru there manually.
Reply:this is because outlook is set as your default mail client. you need to go -start, set programs access and disable outlook as default