It may be because the editor is trying to read the plugin that can't be loaded normally.
Please follow these steps to disable target plugin, and try launching the tool.
(1)Please remove all files except "V3Comp.dll" and "V3Reverb.dll" from VST Plugin folder under VOCALOID3 folder to other place.
The default path of VOCALOID3 folder is as follows.
- For 32bit OS: C:\Program Files\VOCALOID3
- For 64bit OS: C:\Program Files(x86)\VOCALOID3
(2) Please delete following file(s).
* Please note that Application Data folder is classified as "hidden" at the default state.
You need to change the setting of the explorer in order to proceed.
Please see Windows help and/or Microsoft website for more information.
(3) Please launch VOCALOID3 Editor.