Dell e7440, sleep sometimes fails, kernel logs show ACPI errors

Question

I have a new Dell Latitude E7440 with Ubuntu 14.04.2. Sometimes (but not always), after sleeping, I cannot resume, as after trying to resume one of the following happens:

• I can move the mouse but cannot control the keyboard and type my password (and the mouse cursor stays in the shape of an arrow)
• I can't even move the mouse
• I see a black screen

The kernel log shows some errors from the moments when I tried to wake up the computer:

Apr  8 09:10:18 lati kernel: [22586.645486] ACPI Error: Index value 0x0000000000000083 overflows field width 0x7 (20140424/exfldio-343)          
Apr  8 09:10:18 lati kernel: [22586.645489] ACPI Error: Method parse/execution failed [\NEVT] (Node ffff88040e047258), AE_AML_REGISTER_LIMIT (20140424/psparse-536)
Apr  8 09:10:18 lati kernel: [22586.645491] ACPI Error: Method parse/execution failed [\_SB_.PCI0.LPCB.ECDV._Q66] (Node ffff88040e044b90), AE_AML_REGISTER_LIMIT (20140424/psparse-536)

and just after these error messages there's a warning:

Apr  8 09:10:18 lati kernel: [22638.968661] WARNING: CPU: 0 PID: 27214 at /build/buildd/linux-lts-utopic-3.16.0/drivers/gpu/drm/i915/intel_display.c:3324 intel_crtc_wait_for_pending_flips+0x171/0x180 [i915]()

The last message before the sleep was:

Apr  7 23:42:34 lati kernel: [22578.986188] PM: Preparing system for mem sleep

Do you think the kernel logs give any hint to my laptop's sleep issues?

Update

After trying to "sleep" and wake up again, the same problem (can move the mouse but can't click anything or type anything), but the log messages were different this time. This is a small selection of them.

The last message before sleeping:

Apr  8 11:44:08 lati kernel: [ 4736.851598] ahci 0000:00:1f.2: port does not support device sleep

and one line after that, this weirdest line appears (in vim; probably indicating a corruption of the file or something..?)

  ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@Apr  8 13:52:03 lati kernel: [    0.000000] Initializing cgroup subsys cpuset

(the actual line is much longer...)

and a bit later this warning:

Apr  8 13:52:03 lati kernel: [    0.910836] i8042: Warning: Keylock active

The syslog is quite similar. The last two lines before sleeping look like that:

Apr  8 11:44:08 lati kernel: [ 4736.851598] ahci 0000:00:1f.2: port does not support device sleep
Apr  8 11:44:08 lati kernel: [ 4737.399980] init: anacron main process (3054) killed by TERM signal

Then this ^@ line again, and finally those errors and warnings:

Apr  8 13:52:03 lati kernel: [    0.910836] i8042: Warning: Keylock active
Apr  8 13:52:03 lati kernel: [    2.724522] systemd-udevd[352]: Error calling EVIOCSKEYCODE: Invalid argument
Apr  8 13:52:03 lati NetworkManager[727]: <warn> failed to allocate link cache: (-12) Object not found
Apr  8 13:52:03 lati NetworkManager[727]: <warn> /sys/devices/virtual/net/lo: couldn't determine device driver; ignoring...
Apr  8 13:52:03 lati NetworkManager[727]: <warn> Trying to remove a non-existant call id.
Apr  8 13:52:05 lati ModemManager[697]: <warn>  Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:19.0': not supported by any plugin
Apr  8 13:52:05 lati ModemManager[697]: <warn>  Couldn't find support for device at '/sys/devices/pci0000:00/0000:00:1c.3/0000:02:00.0': not supported by any plugin
Apr  8 13:52:08 lati NetworkManager[727]: <warn> dnsmasq not available on the bus, can't update servers.
Apr  8 13:52:08 lati NetworkManager[727]: <error> [1428490328.454641] [nm-dns-dnsmasq.c:396] update(): dnsmasq owner not found on bus: Could not get owner of name 'org.freedesktop.NetworkManager.dnsmasq': no such name
Apr  8 13:52:08 lati NetworkManager[727]: <warn> DNS: plugin dnsmasq update failed
Apr  8 13:52:08 lati dnsmasq[1666]: warning: no upstream servers configured
Apr  8 13:52:08 lati NetworkManager[727]: <warn> dnsmasq appeared on DBus: :1.47
Apr  8 13:52:20 lati ModemManager[697]: <warn>  Could not grab port (tty/ttyS4): 'Cannot add port 'tty/ttyS4', unhandled serial type'
Apr  8 13:52:20 lati ModemManager[697]: <warn>  Couldn't create modem for device at '/sys/devices/pci0000:00/0000:00:16.3': Failed to find primary AT port
Apr  8 13:52:47 lati gnome-session[2016]: GLib-CRITICAL: g_environ_setenv: assertion 'value != NULL' failed