I'm seeing this on nearly every 2010 UK system I come across, including my own.
Open Layout designer, click Field and drag a box on the layout. Field list pops up. Click New and create a new field. Add the field + label to the layout.
At this point get Object reference: Not set to an instance of an object. The screen goes grey and the system hangs. Kill ACT! via task manager. Open ACT!. Open Layout designer. The new field is now available to be added to the layout and can be added successfully.