I have some observations about your script.
Here you have to close with ']'
$('input[name=txtApepaterno').val("prueba");
I notice that first you want to search by input name and then to turn it off you search for id, this will only work unless the input has the same name and id, but I think that the error may come from there.
I take the time to make a functional example for the case you are commenting on.
function setValue() {
$('input[name=txtApepaterno]').val("prueba");
}
function usingProp() {
$("#txtApepaterno" ).prop( "disabled", true );
}
function usingGetElementById() {
document.getElementById("txtApepaterno").disabled = true;
}
function activeInput(){
$( "#txtApepaterno" ).prop( "disabled", false );
}
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
</head>
<body>
<input id="txtApepaterno" name="txtApepaterno" />
<ul>
<li><a href="javascript:setValue();"> Setear valor </a></li>
<li><a href="javascript:usingProp();"> Desactivar usando Prop </a></li>
<li><a href="javascript:usingGetElementById();"> Desactivar usando getElementById </a></li>
<li><a href="javascript:activeInput();"> Volver a activar </a></li>
</ul>
</body>
</html>