OK. I could see the slimnas install was more or less working because the file trees etc were being built. So I decided to re-format my HDD. For some reason I had set the original format to "don't erase MBR" I unchecked this box, reformatted and re-ran the install of slimnas.

Everything is working well. My squeezebox is happily playing music from the NAS.

Thanks again to everyone.