I get this error - slightly different to all the others I've seen as it says "supported" at the end:
GDBus.Error:org.freedesktop.DBus.Error.failed:Operation not supported
Maybe have you set up your home folder to be encrypted at the installation of ubuntu, I will suggest you to have a look at the following website for explanations about how to set up a password instead of a random key for swap encryption: https://help.ubuntu.com/community/EnableHibernateWithEncryptedSwap#Explanation
But before following the explanations from there, I would suggest you to check up if your swap is encrypted, you can do that by typing the following in the terminal:
$ swapon --summary
You should see output similar to:
If you do not see cryptswap1, the partition is either unencrypted or is not encrypted to Ubuntu's standard.