"Swap not available" - I must manually "swapon" after every reboot

I am on Ubuntu 12.04, Thinkpad Edge 13, encrypted home. A message in the System Monitor tells me that swap is "not available". I can get it back using the swapon option in gparted (I thought I could also do sudo swapon -a in a terminal, but that does not work). The problem is that I have to swapon after every reboot. How can I switch it back on so it stays on even after a reboot?

my fstab:

# # <file system> <mount point> <type> <options> <dump> <pass> 
proc /proc proc nodev,noexec,nosuid 0 0 
# / was on /dev/sda5 during installation 
UUID=47641b93-9d12-4e6a-b803-dde28f0e5725 / ext4 errors=remount-ro 0 1

You have no configuration for swap in /etc/fstab. Add following line to that file:

UUID=<uuid> none   swap    sw    0       0   

You have to replace <uuid> with the uuid of your swap partition. To do that, run sudo blkid

$ sudo blkid
/dev/sda1: LABEL="System Reserved" UUID="88A0D0A1A0D09752" TYPE="ntfs" 
/dev/sda2: UUID="0620D9F920D9EFA3" TYPE="ntfs" 
/dev/sda5: UUID="c282b418-2045-4852-8789-88a44360a0bb" TYPE="ext4" 
/dev/sda6: UUID="f99c6a0c-790a-45ca-a1a9-8874f5a2999b" TYPE="ext4" 
/dev/sda7: UUID="4cc2e909-ebd1-4c72-abee-aa32035bf330" TYPE="swap"

This is a list of my partitions, and as you see, /dev/sda7 is my swap partition. So you can copy the value of UUID corresponding to your swap, omitting the quotes, and use it for your fstab file.

After the upgrade to 12.04, certain little anomalies occurred. I was unaware my swap partition wasn't working until I tried to open a large file in Gimp.

blkid shows:

/dev/sdb6: UUID="3e0550cf-4a55-4aa8-80fa-24103c1b25a7" TYPE="swap" 

but it is not active according to System Monitor. The UUID was definitely right but no go ... not sure how I got to this command:

blkid -p /dev/mapper/foo-swap_1
error: /dev/mapper/foo-swap_1: No such file or directory

File manager showed me a 0 byte icon, filename control, -- so what was supposed to be written there? By what?

sudo swapon --all --verbose yielded
swapon: cannot find the device for UUID=3e0550cf-4a55-4aa80fa-24103c1b25a7

I edited the /etc/fstab file adding

/dev/sdb6   none    swap    sw  0   0

Reboot and System Monitor shows it active.

This was the first site I found for help; in my case, the UUID did not work even though it was in fstab, so there is something missing 'in the middle'. This may help someone, who knows.