If you open your 3dsmax and found the UI has been reset or change to other UI, it could be due to:

  • the CUI files are corrupted due to unknown reason
  • last 3dsmax session was not shutdown properly
  • your CUI files are located on the network and you have lost access to it

To reset your UI to default configuration, simply go to Customize > Custom UI and Defaults Switcher...

Custom UI and Defaults Switcher

Then select your preferred UI and restart 3dsmax.

Choose initial settings for tool options and UI layout