Thanks Dave, it is typical of me to fall into a small trap.It’s too late in the UK to think at the moment... I’ll have a look tomorrow.
I would perform a listing of the disk as the first thing rather than attempting to load anything... That’s the LOAD “$”,8 command followed by a LIST.
I noticed when I typed LOAD "*", 8 it loaded the file Aliens! fine, and it works ! This loads the first file.
The example given in the SD2PET user manual says LOAD "filename", 8 , but this does not work. It works though if the extension is added;
So if I type LOAD "Aliens!.prg", 8 it works just fine.
So maybe the instruction should have been LOAD "filename.ext",8 ?