Hey Tasio,
It must be an error or something else from Scriptcase but the input field of the quick search has two elements (inside the Toolbar area) with the same Id and that is why when you try to set the focus it does not know which element is referencing. Anyway, in case you would like to set the focus on other element, you have to add the following line in the Javascript OnLoad event of the Form:
document.getElementById(‘id_sc_field_fieldname’).focus();
Where fieldname is the actual name of your field. This would set the focus to that element.
So, as far as this element (the Quick Search input field), that would be a question the Scriptcase, why it does not allow focus if it is for the multiple elements with the same id or if somehow, somewhere they are blurring the focus through other code, jQuery, etc.
Hope this helps.
Regards,