SharePoint Designer 2013 won't allow inserting webpart zones or web parts - publishing page layout

Hi All,

I am trying to create a custom publishing page layout in SPD 2013 but when I click the insert > webpart zone button SPD just plays an error bleep and does nothing. This also applies to inserting a webpart into the Page Layout.

I've tried as well to create an exact duplicate of a blank web part page and the same issue applied. Any ideas would be appreciated.

Thanks,