You'll need to add a second sub summary layout part "when sorted by" your business name field. Sub summary layout parts are only visible when their "sorted by" field is part of the current sort order and thus sorting by business name makes your sub summary layout part with the letter of the alphabet disappear.
thanks. Can you point me to any tutorial or provide me any more specific details on how to go about this. I will give it a go but at the moment im kind of walking in the dark. thanks.
Since you already have one sub summary layout part set up, I assumed that you would be able to add a second. I'm forgetting that this is a set up found in one of the starter solutions so you probably did not set up the original sub summary part.
Here's a tutorial on summary reports with sub summary layout parts: Creating Filemaker Pro summary reports--Tutorial