The message is intimidating, but it is rarely fatal. In 90% of documented cases, the fix is a combination of repairing .NET Framework, updating graphics drivers, and resetting the user workspace. The remaining 10% require a clean OS-level reinstallation.
If the acngenexe error only happens on a specific drawing, the file database is likely corrupted. Open AutoCAD and type into the command line. i autocad debug error acngenexe full