The problem is in the naming of the function 'start()'
This is a reserved function name and causes the error. Just change the
name of the function, and the reference to the function, and it will work.
eg
<HTML>
<HEAD>
<SCRIPT LANGUAGE="JavaScript">
<!--
...cut...
function strt(){
progCounter = 0
goOn()
}
...cut...
<form name="abc">
<input type="text" name="progtxt" size=3 readonly value="0"> </form> <p>
<span onclick="strt()">Go!</span><br>
<input type="button" value="Go!" onclick="strt()">
</BODY>
</HTML>