The boot partition is not mounted - cannot configure

Raspberry Pi 3
Nextcloud version 12.0.3
Operating system and version:
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 9.1 (stretch)
Release: 9.1
Codename: stretch
Apache version 2.4.25 (Raspbian)
PHP version 5.6.22-2+b3

I have tried several methods of putting an image onto the SD card using Ubuntu desktop.
The result is always the same:
When plugging the card into the pi…
raspi-config:

The boot partition is not mounted - cannot configure.
Note that the raspi-config is intended for use on Raspian
only and cannot be guaranteed to work on other operating
systems.

I have tried Nextcoloudpi, and GUI Stretch.
I’ve done it with dd and Etcher.
No difference.
I’ve mounted it and run raspi-config.
The root is read only.
Reboot, forgotten everything… The boot partition is not mounted - cannot configure etc.etc.

Anyone any ideas?

The new SD card I bought had a partition of 4 MB unallocated at the front.
I deleted it and reformatted.
It worked.