The most recent versions of mmd_tools cause the [Add Display Panel Groups] operator of mmd_tools_helper to not work. Here is the most recent version of mmd_tools which works with mmd_tools helper:
https://github.com/powroupi/blender_mmd_tools/archive/v0.6.0.zip
(You cannot have more than one version of mmd_tools installed in Blender both at the same time, though. )
EDIT: mmd_tools helper should now be compatible with all versions of mmd_tools
The most recent versions of mmd_tools cause the [Add Display Panel Groups] operator of mmd_tools_helper to not work. Here is the most recent version of mmd_tools which works with mmd_tools helper: https://github.com/powroupi/blender_mmd_tools/archive/v0.6.0.zip
(You cannot have more than one version of mmd_tools installed in Blender both at the same time, though. )
EDIT: mmd_tools helper should now be compatible with all versions of mmd_tools