System issue when logging in 18.04 Ubuntu

Hi,
I've just installed Ubuntu 18.04 on my old MacBook early 2008, 2, 5 GB, running on dual-mode.

After logging in there is a recurrent pop message system eror detected, but I know this is only a symptom, not the cause,

so I decided to record the logs. Here are the cryptic lines. Many thanks in advance
Aldo
Here are the cryptic lines:

Logs begin at Thu 2019-09-05 18:40:33 CEST, end at Sat 2019-09-07 19:17:52 CE
Sep 07 19:04:50 aldo-MacBook kernel: Couldn't get size: 0x800000000000000e
Sep 07 19:04:50 aldo-MacBook kernel: MODSIGN: Couldn't get UEFI db list
Sep 07 19:04:50 aldo-MacBook kernel: Couldn't get size: 0x800000000000000e
Sep 07 19:04:50 aldo-MacBook kernel: Couldn't get size: 0x800000000000000e
Sep 07 19:05:01 aldo-MacBook kernel: Unable to load isight firmware
Sep 07 19:05:01 aldo-MacBook kernel: i915 0000:00:02.0: Invalid PCI ROM header s
Sep 07 19:05:01 aldo-MacBook kernel: PKCS#7 signature not signed with a trusted
Sep 07 19:05:02 aldo-MacBook kernel: Bluetooth: hci0: unexpected event for opcod
Sep 07 19:05:12 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_flip_done [
Sep 07 19:05:22 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:05:32 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:06:04 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_flip_done [
Sep 07 19:06:04 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:06:04 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:06:14 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_flip_done [
Sep 07 19:06:24 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:06:35 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:06:38 aldo-MacBook gnome-session-binary[1074]: CRITICAL: Unable to cre
Sep 07 19:06:51 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_flip_done [
Sep 07 19:07:01 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:07:11 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_dependencie
Sep 07 19:07:22 aldo-MacBook kernel: [drm:drm_atomic_helper_wait_for_flip_done [
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