How to Fix AutoCAD Internal Errors: UNDOCMD 3 Explained

BIM Software Tip: How to Fix Internal Errors in AutoCAD: UNDOCMD 3

Issue:

When attempting to save a drawing to a previous version, AutoCAD crashes and displays the following error message:

Internal error: UNDOCMD 3

Cause:

This error typically occurs due to a large number of undo operations stored in the drawing. AutoCAD saves undo information in temporary discard files, usually named ac$$*.ac$. These files are located in the TEMP folder on your computer.

Solution:

To resolve this issue, please follow these steps:

1. Open the Start menu and go to the Search tab.
2. Type %TEMP% and press Enter to open the TEMP folder.
3. Locate and delete all files starting with ac$$ (e.g., ac$$*.ac$).

After clearing these files, you can try disabling the undo function temporarily to test if the issue persists when saving the drawing.

How to disable the undo function in AutoCAD:

Enter the following command in AutoCAD:

UNDO (C) Control (N) None

In some cases, uninstalling Kaspersky antivirus software has also been reported to resolve this problem.

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