Comment 4 for bug 718670

Update and workaround:

I inserted manually into the grub.cfg between the lines:

submenu "Previous Linux versions" {
menuentry 'Ubuntu, mit Linux 2.6.37-12-generic' --class ubuntu --class gnu-linux --class gnu --class os {

submenu "Previous Linux versions" {
set superusers='xxuser_namexx'
password_pbkdf2 xxuser_namexx grub.pbkdf2.sha512.3.DC0E03A0DB4....
menuentry 'Ubuntu, mit Linux 2.6.37-12-generic' --class ubuntu --class gnu-linux --class gnu --class os {

Now I will be asked to put in the user_name and the password, if I press the key "C" or "E" respectively.

I hope it will help to find a final solution.