The in AutoCAD (and AutoCAD LT) typically points to a conflict between older software versions and modern operating systems like Windows 11, or a corrupted installation. This specific file is an ObjectDBX module related to 3D modeling and object data; when it fails to load or encounters a memory violation, the application crashes immediately. Best Fixes for "acismobj20.dbx" Fatal Errors
handles 3D objects and regions, the error often stems from a corrupt entity in your Recover Command : Open a blank AutoCAD session and type autocad fatal error acismobj20dbx best
Use _EXPLODE on suspect 3D solids to convert them to 3D faces, then re-extrude. This breaks the ACIS corrupt chain. FATAL ERROR: acismobj20