Button targets new window instead of frame! HELP!

1

I have a menu in one of the frames on my site, and when you press the different links, you should see the page in the mainFrame, but it just opens in a new window!

this is the frameset:

  
<frameset rows="140,*,65" cols="*" framespacing="0" frameborder="no" border="0">
    <frame src="bkTop.html" name="topFrame" noresize="noresize" id="topFrame" title="topFrame" />
    <frame src="bkHome.html" name="mainFrame" scrolling="yes" noresize="noresize" id="mainFrame" title="mainFrame" />
    <frame src="bkBottom.html" name="bottomFrame" noresize="noresize" id="bottomFrame" title="bottomFrame" />
</frameset>

and this is the AS for the menubuttons:

on  (release)  {
getURL("bkWeb.html", "mainFrame");
}

what can I have done wrong? I really need this to work asap!