Hide duration field based on another field value

Hi!

 I am getting errors, while I want to hide duration field on the form using this javascript:

function lockdurationfield() {
var duration = Xrm.Page.getControl("actualdurationtime").getName();
var category = Xrm.Page.getAttribute("csp_category").getValue();
if (category == 862600001) {

duration.setDisabled(true);
}
}

I added action on Form (OnLoad).

Thank you for any help!