In javascript, what is an undefined error? The report is saying one of my images is undefined (it's for a mouseover effect) - the code is pasted below.

<script language="JavaScript" type="text/javascript">
<!--
browserName = navigator.appName;
browserVar = parseInt ( navigator.appVersion );
version = "n2";
if ( browserName == "Netscape" && browserVer >= 3 ) version = "n3";
if ( broswerName == "Microsoft Internet Explorer" && browserVer >=4 ) version ="e4";
if ( version == "n3" version == "e4" )
{
blank = new Image(163,34);
blank.src = "../../../images/comms%20news/blank.gif";

about = new Image(163,34);
about.src = "../../../images/comms%20news/about.gif";

pubs = new Image(163,34);
pubs.src = "../../../images/comms%20news/pubs.gif";

info = new Image(163,34);
info.src = "../../../images/comms%20news/info.gif";

press = new Image(163,34);
press.src = "../../../images/comms%20news/press.gif";

marketing = new Image(163,34);
marketing.src = "../../../images/comms%20news/marketing.gif";

web = new Image(163,34);
web.src = "../../../images/comms%20news/web.gif";

ni = new Image(163,34);
ni.src = "../../../images/comms%20news/ni.gif";

scotland = new Image(163,34);
scotland.src = "../../../images/comms%20news/scotland.gif";

wales = new Image(163,34);
wales.src = "../../../images/comms%20news/wales.gif";
}
function button_on ( imgName )
{
if ( version == "n3" version == "e4" )
{
butOn = eval ( imgName + "_on.src" );
document [imgName].src = butOn;
}
}
function button_off ( imgName )
{
if ( version == "n3" version == "e4" )
{
butOff = eval ( imgName +"_off.src" );
document [imgName].src = butOff;
}
}
// -->
</script>



<a href="info.htm"
onMouseOver = "
blank.src = info.src;
window.status='info'; return true"
onMouseOut = "
blank.src = blank2.src;
window.status =' ';
return true"><img src="../../../images/comms%20news/three.jpg" border=0 width="30" height="34" name="info"></a></td>