Appreciate your comments.
The thing is I had managed to get Excel to write back to the file at a client site.
This would have been at least 5 or 6 years ago. Naturally I have forgotten how I got it working
I remember it worked because I had to change the definition in the dictionary of a two-part key to the file.
It was stockcode 25 chars plus warehouse 2 chars.
Oh well. I'll try and find a MS Excel forum that might help.