Disable Button control

Hi Experts,

I want to disable the the delivery remainder of purchase order according to the parameter created.
Written my code in event handler On activate.But I didn't got correct output, But when I am Using visible It's working.
can anyone one suggest me the way to do this.

[FormEventHandler(formStr(PurchTable), FormEventType::Activated)]
public static void PurchTable_OnActivated(xFormRun sender, FormEventArgs e)
{
FormControl PurchUpdateRemain = sender.design(0).controlName(#PurchUpdateRemain);


if(MyParameterTable::find().MyControl == NoYes::Yes)
{
PurchUpdateRemain.enabled(false);
}
else
{
PurchUpdateRemain.enabled(true);
}
}

Thanks

Tanmay