Thank you for your quick response.
I have deleted the backup file I sent you and backed up the project again. Having looked at the new backup file, the same issue has occurred.
I pay for OneDrive (as part of Office 365) and other videos with larger file sizes have uploaded to OneDrive perfectly in the past, so the size shouldn't be the issue.
The project plays as expected on the timeline within VideoPad, it is only when I export the video that I have issues. I am using version 13.59, downloaded from the link that you sent to the user borate on 4th Aug above (I think it is the same version I was already using anyway). Having read through this thread I have tried running it as administrator and that has also made no difference.
New backup file here: 2023-08-22 16-11-41 file backup
Is there anything else I can try?
Thank you.