Move one of the objects a very tiny amount (e.g., 0.001 units) so their faces no longer perfectly overlap. This often clears the mathematical bottleneck. Run SOLIDCHECK: Set the system variable SOLIDCHECK
If the above steps don't resolve Autocad Error 18003, you may need to perform more advanced troubleshooting: autocad error 18003
Boolean calculation failure due to invalid solid intersections or blocks. Explode blocks; fix coincident faces; eliminate micro-gaps. The selected object is not a valid 3D Solid. Use SOLIDEDIT to check integrity; rebuild from 2D profiles. Error 18026 Move one of the objects a very tiny amount (e
: Attempting Boolean operations on Block References instead of native 3D Solids. Troubleshooting and Resolutions fix coincident faces
If the internal engine indicates self-intersection, you need to break the object down into simpler forms.
