"Unable to open customization file.." error and ribbon not loading in AutoCAD Products

Autodesk Support

Feb 18, 2025

Products and versions covered

Issue:

When launching AutoCAD, the following error is displayed and then no ribbon shows in the program:

AutoCAD

Unable to open customization file: C:\Users\<user>\AppData\Roaming\Autodesk\C3D 2020\enu\Support\c3d.cuix
This file has been moved, renamed, or deleted. To find and reload this file, type CUILOAD at the Command prompt.

AutoCAD error window "Unable to open customization file: C:\Users\<user>\AppData\Roaming\Autodesk\C3D 2020\enu\Support\c3d.cuix"

 
Note: The error message will differ to reflect the affected AutoCAD product CUIx file.
 

Causes:

Damaged or missing CUIx file.

Solution:

To resolve the issue try out the following: 

AutoCAD

Copy a new CUIx file from the UserDataCache folder:

  1. Exit AutoCAD.
  2. In Windows Explorer, navigate to C:\ProgramFiles\Autodesk\AutoCAD 20xx\<program name>\UserDataCache\Support. For plain AutoCAD, disregard the "<program name>" subfolder.
  3. Copy the affected CUIx file and paste it into C:\Users\<user>\AppData\Roaming\Autodesk\AutoCAD 20xx\enu\Support. For AutoCAD vertical products, the "AutoCAD 20xx" folder will reflect the program's name, such as "C3D 2020" for Civil 3D 2020. 

Note: The UserDataCache and AppData folders are hidden folders (see How to turn on hidden files and folders).

AutoCAD Architecture and MEP

The ACA.cuix and MEP.cuix are not located in the UserDataCache folder, which is why a working version of said files needs to be taken from a different Windows profile or from a separate machine.

Reset AutoCAD to Defaults

Reset the AutoCAD product to default (See How to reset AutoCAD to default).

Products:

AutoCAD Products;

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