JS - Undefined error

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">
= 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>