Hi
Eventually this might help: ssh - sudo: no tty present and no askpass program specified - Ask Ubuntu
OTOH, if you can afford such an entry in sudoers, why not enable the root account?
After you get past this step, expect another issue (Ubuntu 14 is not supported by converter 5.5 after all). Converter calls "grub-install -v" to get the grub version. However in Ubuntu 14, this is done by "grub-install -V". You may work around by renaming the original file and adding a script to call it, a script that can handle the "-v" argument.
HTH
Plamen