I tried reactivating the hibernate option when it was disabled, i tested sudo pm-hibernate and it was ok, but after that when i hibernate this appears "not enough free swap". so i would like to disable the hibernate option again. help!
Better yet, if you want to enable a functional hibernate menu entry, you must first make sure you have a large enough swap partition and that it is correctly assigned to Ubuntu 12.04. Only then you should enble hibernate through a simple modification of the /var/lib/polkit-1/localauthority/10-vendor.d/com.ubuntu.desktop.pkla file.
Run GParted and check the size of your swap partition, assuming there's one. It should be larger than your physical RAM. i.e. I had the same problem as I didn't provide a swap partition when I installed assuming my RAM was sufficient. I have 6GB RAM so I had to create a 12GB swap partition.
I did it after the install, so Ubuntu didn't automatically recognized and I had to assign it following this instructions:
Then, from the same site, I followed the instructions to enable it for hibernation and resume, modifying my Grub config file and created another called initramfs.
Lastly, I followed the instructions here to place a Hibernate entry in the system menu.
Actually, I did the very last step first and the hibernation process was spotty until I enlarged the swap to double the RAM (started with basically the same amount as RAM) and went through the steps described in the first step.
For me it was a bit involved because I had to go trial & error to troubleshoot the process but you should have no problem by going in the order suggested above.
Let us know how it went.