"Internal error generation!
Internal Error: AT_Data (153): The line 1 contains a node, which is not in the macro element 1"

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Here's my simple arch:

1. Line 1 and 2 represent the arch lines, line 3 and 4 the "short" horizontal lines that close up to the boundary to form arch macro-element 1. Line 1 is the "boundary" between the arch and the filler macro-elements.

2. Line 5 and 7 are vertical lines that enclosed the filler vertically, while horizontal line 6 close up the boundary to form filler macro-element 2.

3. Across the thickness of arch (line 3 and 4), a refinement by 6 number of elements was specified.

4. Across the circumference of arch (line 1 and 2), a refinement of 100 number of elements was specified.

5. Across the depth of filler (line 5 and 7), a refinement of 100 number of elements was specified.

6. Across the longitudinal arch bridge model (line 6), a refinement of 100 number of elements was specified.

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Note:
When no refinement was specified for line 5 and 7, mesh generation was able to be carried out without error message, but the mesh is unacceptable (hence the refinement).

Many thanks for the assistance.