> ## Documentation Index
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# Invalid combination/design curve, not all elements could be mapped

## Issue:

This error popped up when I tried to run a Topology Optimization using the Extrusion Constraint: Invalid combination/design curve, not all elements could be mapped.

## Cause:

The section of the part along the curve has to be constant in order for the **Extrusion Constraint** to work properly.

## Solution:

Change the starting part to have a constant thickness along the curve.

## Keywords:

*error design topology optimization constraint extrusion curve elements not issue invalid combination mapped*