Comment 1 for bug 691834

I've just got this problem after updating the Natty Kubuntu kernel to 2.6.38-5-generic #32-Ubuntu SMP Tue Feb 22 16:10:15 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux from 2.6.38-3. I have a number of partitions (1 of which is Kubuntu and 2 Ubuntu). The Lucid Lynx Partition (sdb5) is not shown in the grub2 menu list, but is still there as shown by
$ sudo blkid
[sudo] password for kevin:
/dev/sda1: UUID="F8D82972D8292FF4" TYPE="ntfs"
/dev/sda5: LABEL="Music" UUID="C82C72412C722B18" TYPE="ntfs"
/dev/sda6: LABEL="Data" UUID="9660546760544FDB" TYPE="ntfs"
/dev/sda7: UUID="6c104125-11d8-4775-9206-5dc82915e422" TYPE="swap"
/dev/sda8: LABEL="KB-NN" UUID="5bea48eb-932d-4a3f-97db-d11747762eab" TYPE="ext4"
/dev/sdb1: LABEL="ISO-FILES" UUID="4A47-915E" TYPE="vfat"
/dev/sdb5: UUID="d2d5bde7-c446-486e-9f16-a47239e21e0e" TYPE="ext4" *** Lucid Lynx ""
/dev/sdb6: UUID="f20905e7-7193-4134-833a-95456f61cc93" TYPE="ext4"
$ sudo fdisk -l

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x46c446c3

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 10199 81923436 7 HPFS/NTFS
/dev/sda2 10200 19457 74364854+ f W95 Ext'd (LBA)
/dev/sda5 10200 11475 10249438+ 7 HPFS/NTFS
/dev/sda6 11476 13522 16442496 7 HPFS/NTFS
/dev/sda7 18242 19457 9767488+ 82 Linux swap / Solaris
/dev/sda8 13523 18241 37904384 83 Linux

Partition table entries are not in disk order

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0673fa40

   Device Boot Start End Blocks Id System
/dev/sdb1 1 5099 40957686 b W95 FAT32
/dev/sdb2 5100 30387 203125626+ 5 Extended
/dev/sdb5 19689 30387 85939686 83 Linux *** Lucid Lynx ***
/dev/sdb6 5100 19688 117185536 83 Linux

Partition table entries are not in disk order
$

I've commented the Lucid Lynx partition that is not shown in grub above.
A sudo update-grub does not recover the missing entry.