The error i get after choosing Ubuntu in grub2 is:

error: file not found.
error: file not found.
error: file not found.
Press any key to continue ...

here is my grub.cfg:

$ cat grub.cfg 
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"

if [ x"${feature_menuentry_id}" = xy ]; then
  menuentry_id_option="--id"
else
  menuentry_id_option=""
fi

export menuentry_id_option

if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
  if [ x$feature_all_video_module = xy ]; then
    insmod all_video
  else
    insmod efi_gop
    insmod efi_uga
    insmod ieee1275_fb
    insmod vbe
    insmod vga
    insmod video_bochs
    insmod video_cirrus
  fi
}

if [ x$feature_default_font_path = xy ] ; then
   font=unicode
else
insmod part_msdos
insmod ext2
set root='hd0,msdos2'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos2 --hint-efi=hd0,msdos2 --hint-baremetal=ahci0,msdos2  ea06e8dd-40ce-482a-8dd2-be2b88635892
else
  search --no-floppy --fs-uuid --set=root ea06e8dd-40ce-482a-8dd2-be2b88635892
fi
    font="/usr/share/grub/unicode.pf2"
fi

if loadfont $font ; then
  set gfxmode=auto
  load_video
  insmod gfxterm
  set locale_dir=$prefix/locale
  set lang=en_US
  insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=5
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
if background_color 44,0,30; then
  clear
fi
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
function gfxmode {
	set gfxpayload="${1}"
	if [ "${1}" = "keep" ]; then
		set vt_handoff=vt.handoff=7
	else
		set vt_handoff=
	fi
}
if [ "${recordfail}" != 1 ]; then
  if [ -e ${prefix}/gfxblacklist.txt ]; then
    if hwmatch ${prefix}/gfxblacklist.txt 3; then
      if [ ${match} = 0 ]; then
        set linux_gfx_mode=keep
      else
        set linux_gfx_mode=text
      fi
    else
      set linux_gfx_mode=text
    fi
  else
    set linux_gfx_mode=keep
  fi
else
  set linux_gfx_mode=text
fi
export linux_gfx_mode
menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-ea06e8dd-40ce-482a-8dd2-be2b88635892' {
recordfail
	load_video
	gfxmode $linux_gfx_mode
	insmod gzio
	insmod part_msdos
	insmod ext2
	set root='hd0,msdos1'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  f186e672-0f46-46fe-ad89-34620ea571b2
	else
	  search --no-floppy --fs-uuid --set=root f186e672-0f46-46fe-ad89-34620ea571b2
	fi
	linux	/vmlinuz-3.8.0-5-generic root=UUID=ea06e8dd-40ce-482a-8dd2-be2b88635892 ro   quiet splash nomodeset nmi_watchdog=0 $vt_handoff
	initrd	/initrd.img-3.8.0-5-generic
}
submenu 'Advanced options for Ubuntu' $menuentry_id_option 'gnulinux-advanced-ea06e8dd-40ce-482a-8dd2-be2b88635892' {
	menuentry 'Ubuntu, with Linux 3.8.0-5-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.8.0-5-generic-advanced-ea06e8dd-40ce-482a-8dd2-be2b88635892' {
	recordfail
		load_video
		gfxmode $linux_gfx_mode
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd0,msdos1'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  f186e672-0f46-46fe-ad89-34620ea571b2
		else
		  search --no-floppy --fs-uuid --set=root f186e672-0f46-46fe-ad89-34620ea571b2
		fi
		echo	'Loading Linux 3.8.0-5-generic ...'
		linux	/vmlinuz-3.8.0-5-generic root=UUID=ea06e8dd-40ce-482a-8dd2-be2b88635892 ro   quiet splash nomodeset nmi_watchdog=0 $vt_handoff
		echo	'Loading initial ramdisk ...'
		initrd	/initrd.img-3.8.0-5-generic
	}
	menuentry 'Ubuntu, with Linux 3.8.0-5-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.8.0-5-generic-recovery-ea06e8dd-40ce-482a-8dd2-be2b88635892' {
	recordfail
		load_video
		insmod gzio
		insmod part_msdos
		insmod ext2
		set root='hd0,msdos1'
		if [ x$feature_platform_search_hint = xy ]; then
		  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  f186e672-0f46-46fe-ad89-34620ea571b2
		else
		  search --no-floppy --fs-uuid --set=root f186e672-0f46-46fe-ad89-34620ea571b2
		fi
		echo	'Loading Linux 3.8.0-5-generic ...'
		linux	/vmlinuz-3.8.0-5-generic root=UUID=ea06e8dd-40ce-482a-8dd2-be2b88635892 ro recovery nomodeset 
		echo	'Loading initial ramdisk ...'
		initrd	/initrd.img-3.8.0-5-generic
	}
}

### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###

### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
	insmod part_msdos
	insmod ext2
	set root='hd0,msdos1'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  f186e672-0f46-46fe-ad89-34620ea571b2
	else
	  search --no-floppy --fs-uuid --set=root f186e672-0f46-46fe-ad89-34620ea571b2
	fi
	linux16	/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
	insmod part_msdos
	insmod ext2
	set root='hd0,msdos1'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1  f186e672-0f46-46fe-ad89-34620ea571b2
	else
	  search --no-floppy --fs-uuid --set=root f186e672-0f46-46fe-ad89-34620ea571b2
	fi
	linux16	/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry 'Windows 7 (loader) (on /dev/sda4)' --class windows --class os $menuentry_id_option 'osprober-chain-CA92FC8F92FC80ED' {
	insmod part_msdos
	insmod ntfs
	set root='hd0,msdos4'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos4 --hint-efi=hd0,msdos4 --hint-baremetal=ahci0,msdos4  CA92FC8F92FC80ED
	else
	  search --no-floppy --fs-uuid --set=root CA92FC8F92FC80ED
	fi
	chainloader +1
}
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/30_uefi-firmware ###
### END /etc/grub.d/30_uefi-firmware ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  ${config_directory}/custom.cfg ]; then
  source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

cheers,
Michael