Autocad Fatal Error Acismobj20dbx Best ((top)) May 2026

Resolving the AutoCAD Fatal Error: Unhandled Access Violation in acismobj20.dbx

Among the most disruptive errors an AutoCAD user can encounter is the fatal exception: "Unhandled Access Violation Reading 0x0000 Exception at [address]" , specifically naming the module acismobj20.dbx . This error typically causes an immediate, unsaved crash when attempting to modify, save, or even select 3D solids or complex 2D regions. Understanding its cause and the most effective solutions is essential for any CAD professional.

Conclusion: You have the best tools now

The acismobj20dbx fatal error is not a death sentence for your project. It is a specific failure in AutoCAD’s 3D solid modeling kernel. By resetting your profile, installing the hotfix, purging the drawing, disabling preview, and fixing your GPU, you have all the best solutions at your fingertips.

Final Pro Tip: Bookmark this page. When the error reappears (and it will, because Autodesk updates slowly), run through Fix #1 through #5 in order. You will be back to modeling in less than 10 minutes.

Have a different fatal error? Check our guides on acge20dbx and heidi9.dll failures.

The AutoCAD Fatal Error associated with acismobj20.dbx is a critical crash that typically occurs during software launch or when handling complex 3D objects. This specific .dbx file belongs to the ASM (Autodesk Shape Manager), the 3D modeling engine used by AutoCAD to process geometry. Core Causes

Version Incompatibility: Most commonly seen when running older AutoCAD versions (like 2015/2016) on newer operating systems like Windows 11. autocad fatal error acismobj20dbx best

File Corruption: Either the program file itself or the specific .dwg file being opened is damaged.

Permission Issues: Lack of full administrator privileges to the installation folder.

Driver Conflicts: Outdated or uncertified graphics card drivers often trigger fatal errors during geometry rendering. Proven Solutions To resolve this, follow these steps in order: Troubleshooting AutoCAD LT 2016 Errors - JustAnswer

4. Rename or Remove the acismobj20.dbx File (Last Resort)

This is risky but sometimes effective if the file itself is corrupted.

• Navigate to: C:\Program Files\Autodesk\AutoCAD 20xx\
• Rename acismobj20.dbx to acismobj20.dbx.old
• Run Repair from the original installer (Control Panel > Programs > Autodesk AutoCAD > Uninstall/Change > Repair). This forces a fresh copy of the module.

Step C: Replace the File (If Registration Fails)

If you get "The module failed to load", the file is physically corrupt. The AutoCAD Fatal Error associated with acismobj20

1. Download a clean copy from an official Autodesk installation source (do not use random DLL websites – obtain from a colleague with the same version or re-extract from the original installer using 7-Zip).
2. Rename the old file to acismobj20dbx.old.
3. Copy the clean file into the folder.
4. Run regsvr32 again.

Step 5 – Run ACIS Recovery Tools

Inside AutoCAD, on the offending drawing:

AUDIT (yes to fix errors)
-ACISOUT (export all ACIS entities to .sat)
ERASE → ALL → Remove (then paste from original)

If that fails, use:

ACISIN (re-import the .sat into a new drawing)

Fix #3: The Drawing Purge (Best for a single corrupted file)

If the error only happens in one specific DWG file, the file itself contains a "poisoned" 3D solid.

The Best Command Sequence: Open AutoCAD in safe recovery mode (hold Shift while double-clicking the DWG and choose "Recover").

Then, run these commands in order:

1. AUDIT > Yes (Fix errors)
2. -PURGE > Type R (Regapps) > * > N (No to each)
3. -PURGE > Type A (All) > * > N
4. ZOOM > EXTENTS
5. EXPLODE (Select all 3D solids – this breaks the complex history tree into basic faces).
6. SAVEAS > Rename the file (e.g., Clean_Copy.dwg).

Warning: Exploding solids removes parametric history, but it kills the fatal error dead.

If All Else Fails: Nuclear Options

• Perform a Clean Uninstall/Reinstall of AutoCAD using the Microsoft Program Install and Uninstall troubleshooter, then the Autodesk uninstall tool, then reinstall.
• Reset AutoCAD to Defaults via the Windows Start Menu → Autodesk folder → “Reset Settings to Default”.
• Consider a different approach to the 3D model: If a specific 3D object is corrupt, you may need to re-model it from scratch in a clean file, or use the EXPLODE command repeatedly to break it down into basic faces.

3.2. Operating System Patch Conflicts

Microsoft Windows updates frequently modify underlying C++ Redistributable libraries or .NET frameworks. AutoCAD depends on specific versions of these libraries. A Windows Update that patches the MSVCRT (Microsoft C Runtime) can create a version mismatch for the acismobj20dbx.arx module, leading to a startup crash.

When to give up (Best last resort)

If you have tried all 5 fixes above and the acismobj20dbx error still appears, the file is likely unrecoverable.

Your best exit strategy:

1. Open the file in AutoCAD LT (which does not use ACIS – it will ignore the solids but keep the linework).
2. Use eTransmit to send the file to a colleague with a different AutoCAD version.
3. Use Rhino 3D or BricsCAD to open the file. These have more robust ACIS readers. Export from there as a DWG 2013 format and re-import.