This is something which works fine:

document.frm("chkD123456").checked=false;

Now my problem is that I want to make the ("chkD123456") dynamic. I have written something like this

var var1 = "chkD" + e.name.substring(5,10)
document.frm(var1).checked=false;

But this does not work, I have got a message saying that document.frm(....) is not an object