It takes time to generate a PDF and while that PDF is being generated, the script moves on and executes the rest of the script. Thus, it is possible that the PDF has not yet been created at the time that the SendMail step executes. Add a Pause/Resume step in to pause the script for a short time after the Save as PDF step and see if that makes a difference.
Thanks. I will try that.
The answer for this particular issue was that I should have used "SMTP" instead of "email client". All is well again!
I don't understand why, but then I am not great at understanding email servers.
Thanks for your response.