EDIT: I have appended the output of cat /etc/default/grub to the question below

This was in fact the key to solving the issue. I think it's worth noting that not having quotes around the OS assigned to GRUB_DEFAULT in /etc/default/grub didn't actually present a problem for quite some time after I had set it(months). This may be because GRUB_DEFAULT was initially set from another linux in my dual boot setup.

I have looked at other questions regarding this error, but haven't found one that helps me, so far.

I am getting the below error when I do:

sudo apt-get upgrade

or a dist-upgrade

I have tried purging the packages mentioned in the error(as per answers to other questions with the same error)

linux-image-extra-3.19.0-25-generic

linux-image-3.19.0-25-generic

with

sudo apt-get remove --purge <the packages>

and

sudo dpkg --purge <the packages>

But in both instances, I get basically the same error output as below. Can anyone help me resolve this?

Error:

yerman@DeepThought:~$ sudo apt-get upgrade

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Calculating upgrade... Done

The following packages will be REMOVED

  linux-image-3.19.0-25-generic linux-image-extra-3.19.0-25-generic

0 to upgrade, 0 to newly install, 2 to remove and 0 not to upgrade.

5 not fully installed or removed.

After this operation, 209 MB disk space will be freed.

Do you want to continue? [Y/n] y

(Reading database ... 529837 files and directories currently installed.)

Removing linux-image-extra-3.19.0-25-generic (3.19.0-25.26) ...

depmod: FATAL: could not load /boot/System.map-3.19.0-25-generic: No such file or directory

run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

update-initramfs: Generating /boot/initrd.img-3.19.0-25-generic

grep: /boot/config-3.19.0-25-generic: No such file or directory

depmod: WARNING: could not open /tmp/mkinitramfs_6wsANd/lib/modules/3.19.0-25-generic/modules.order: No such file or directory

depmod: WARNING: could not open /tmp/mkinitramfs_6wsANd/lib/modules/3.19.0-25-generic/modules.builtin: No such file or directory

run-parts: executing /etc/kernel/postinst.d/pm-utils 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

run-parts: executing /etc/kernel/postinst.d/unattended-upgrades 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

run-parts: executing /etc/kernel/postinst.d/update-notifier 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

/usr/sbin/grub-mkconfig: 6: /etc/default/grub: Syntax error: "(" unexpected

run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 2

dpkg: error processing package linux-image-extra-3.19.0-25-generic (--remove):

 subprocess installed post-removal script returned error exit status 1

Removing linux-image-3.19.0-25-generic (3.19.0-25.26) ...

Examining /etc/kernel/postrm.d .

run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

update-initramfs: Deleting /boot/initrd.img-3.19.0-25-generic

run-parts: executing /etc/kernel/postrm.d/zz-update-grub 3.19.0-25-generic /boot/vmlinuz-3.19.0-25-generic

/usr/sbin/grub-mkconfig: 6: /etc/default/grub: Syntax error: "(" unexpected

run-parts: /etc/kernel/postrm.d/zz-update-grub exited with return code 2

Failed to process /etc/kernel/postrm.d at /var/lib/dpkg/info/linux-image-3.19.0-25-generic.postrm line 328.

dpkg: error processing package linux-image-3.19.0-25-generic (--remove):

 subprocess installed post-removal script returned error exit status 1

Errors were encountered while processing:

 linux-image-extra-3.19.0-25-generic

 linux-image-3.19.0-25-generic

E: Sub-process /usr/bin/dpkg returned an error code (1)

Output of cat /etc/default/grub

# If you change this file, run 'update-grub' afterwards to update

# /boot/grub/grub.cfg.

# For full documentation of the options in this file, see:

#   info -f grub -n 'Simple configuration'



GRUB_DEFAULT=Windows 7 (loader) (on /dev/sda2)

#GRUB_HIDDEN_TIMEOUT=0

GRUB_HIDDEN_TIMEOUT_QUIET=true

GRUB_TIMEOUT=30

GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`

GRUB_CMDLINE_LINUX_DEFAULT="acpi=noirq acpi=force apm=power_off"

GRUB_CMDLINE_LINUX=""



# Uncomment to enable BadRAM filtering, modify to suit your needs

# This works with Linux (no patch required) and with any kernel that obtains

# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)

#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"



# Uncomment to disable graphical terminal (grub-pc only)

#GRUB_TERMINAL=console



# The resolution used on graphical terminal

# note that you can use only modes which your graphic card supports via VBE

# you can see them in real GRUB with the command `vbeinfo'

#GRUB_GFXMODE=640x480



# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux

#GRUB_DISABLE_LINUX_UUID=true



# Uncomment to disable generation of recovery mode menu entries

#GRUB_DISABLE_RECOVERY="true"



# Uncomment to get a beep at grub start

#GRUB_INIT_TUNE="480 440 1"