How to enable a disabled text field?

That is the only working solution for Me:

var allfield7s = document.getElementsByName("field07");
for (var i = 0; i < allfield7s.length; i++)
    allfield7s[i].removeAttribute("disabled");

To access this element in a more standard way, use document.getElementById with setAttribute

document.getElementById("field07").setAttribute("disabled", false);

EDIT

Based on your comment, it looks like field07 is a name, not an id. As such, this should be what you want:

var allfield7s = document.getElementsByName("field07");
for (var i = 0; i < allfield7s.length; i++)
    allfield7s[i].setAttribute("disabled", false);