Instead, use the following free, verified troubleshooting steps to repair the software correctly. Step-by-Step Methods to Fix the Error for Free

The safest way to get a "fresh" copy of AcIsmObj20.dbx is to let the Autodesk installer fix itself. You do not need to uninstall the program. Open the on your Windows machine. Go to Programs and Features . Find your version of AutoCAD in the list. Click Uninstall/Change . When the setup window appears, select Repair or Reinstall .

To prevent future fatal errors, always keep your software updated through official Autodesk channels. Avoid downloading free utility files from search engines, back up your drawing files regularly, and use the built-in AUDIT tool to maintain clean 3D geometry. To help find the exact cause, tell me: What and Windows version are you running?