I have dm900 and have just tried to update image and failed miserably. I have japhar sim installed and this is what I get on the log.
The image is:
openpli-enigma2-7.1Star-dm900_Japhar_v6_GStreamer_1.17.0.1_20190921.rootfs.tar

[*] Mounting '/dev/mmcblk0p2' to '/mnt'
[*] Extracting '/tmp/A4pQUe' to '/mnt'
[*] Mounting '/dev' to '/mnt/dev'
[*] Mounting '/proc' to '/mnt/proc'
[*] Mounting '/run' to '/mnt/run'
[*] Mounting '/sys' to '/mnt/sys'
[*] Mounting '/tmp' to '/mnt/tmp'
Warning: Could not read CA!
Warning: Please consider updating your rescue loader!
/usr/sbin/flash-kernel: line 100: stat: not found
sh: bad number
Fatal: Kernel image is too big
Fatal: Failed to run kernel-image.postinst
[*] Unmounting '/mnt/tmp'
[*] Unmounting '/mnt/sys'
[*] Unmounting '/mnt/run'
[*] Unmounting '/mnt/proc'
[*] Unmounting '/mnt/dev'
[*] Unmounting '/mnt'

What am I doing wrong?