Mixture, thank you, there was no attachment returned with the e-mail, just text, but it was a 'reply' to one I had sent with a photograph attached by Picasa the day before. This was just a note of thanks and the usual 'company disclaimer' at the bottom, which is normal from this source and never been a problem before.
The previous occasion was an original e-mail, i.e. not a reply to one of mine, and contained no attachment, again a regular correspondent.
Whatever the reason, I don't see why it was possible to open normally on the laptop, but not the desktop or iPad ?
Thanks.