Ubuntu grub couldn't see another Linux such as Fedora

Could you give us more information? What version of Ubuntu? What version of grub? Pasting /boot/grub/grub.cfg would help, as that will show us what grub thinks is there.

Ubuntu 10.10 Alpha 3 (GRUB2)
Fedora 13 (GRUB)

#/boot/grub/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 $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"
if [ "${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 {
  insmod vbe
  insmod vga
  insmod video_bochs
  insmod video_cirrus
}

insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set 935cf97e-5c17-4c29-b4b2-1ed41e0c3482
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi
if terminal_output gfxterm ; then true ; else
  # For backward compatibility with versions of terminal.mod that don't
  # understand terminal_output
  terminal gfxterm
fi
insmod part_msdos
insmod ext2
set root='(hd0,msdos1)'
search --no-floppy --fs-uuid --set 935cf97e-5c17-4c29-b4b2-1ed41e0c3482
set locale_dir=($root)/boot/grub/locale
set lang=ru
insmod gettext
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=10
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
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'Ubuntu, with Linux 2.6.35-14-generic-pae' --class ubuntu --class gnu-linux --class gnu --class os {
 recordfail
 load_video
 set gfxpayload=keep
 insmod part_msdos
 insmod ext2
 set root='(hd0,msdos1)'
 search --no-floppy --fs-uuid --set 935cf97e-5c17-4c29-b4b2-1ed41e0c3482
 linux /boot/vmlinuz-2.6.35-14-generic-pae root=UUID=935cf97e-5c17-4c29-b4b2-1ed41e0c3482 ro quiet splash
 initrd /boot/initrd.img-2.6.35-14-generic-pae
}
menuentry 'Ubuntu, with Linux 2.6.35-14-generic-pae (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
 recordfail
 load_video
 set gfxpayload=keep
 insmod part_msdos
 insmod ext2
 set root='(hd0,msdos1)'
 search --no-floppy --fs-uuid --set 935cf97e-5c17-4c29-b4b2-1ed41e0c3482
 echo 'Loading Linux 2.6.35-14-generic-pae ...'
 linux /boot/vmlinuz-2.6.35-14-generic-pae root=UUID=935cf97e-5c17-4c29-b4b2-1ed41e0c3482 ro single
 echo 'Loading initial ramdisk ...'
 initrd /boot/initrd.img-2.6.35-14-generic-pae
}
### 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)'
 search --no-floppy --fs-uuid --set 935cf97e-5c17-4c29-b4b2-1ed41e0c3482
 linux16 /boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
 insmod part_msdos
 insmod ext2
 set root='(h...

That's a little odd.

For a quick fix, try running sudo update-grub. Judging by your grub list, grub only scanned the 10.10 partition during install. I'll take a look at the grub source for Maverick for anything odd.

"sudo update-grub" nothing added, except menu item, that I wroute in /etc/grub.d/40_custom