Error "BMElemSeq[index]: outdated internal index table, run ensure_lookup_table() first" When Exporting to FDS

[phart1]

I receive the above error when trying to export the NIST FDS case. Blender file attached with added txt extension that needs to be removed.

Interestingly, when I use Modifier, Generate, Subdivision Surface on the object I am able to export to FDS.

Error.blend.txt

[emanuelegissi]

Hi, first of all , I need to reproduce your bug here.

So please tell me its exact conditions:

• attach the most simplified blender file that causes the error,
• tell me what blender version you are using, and in what platform (Win, Linux, ...).

[phart1]

I have attached the most simplified blender file.

I am using Windows 11 and Blender 4.4.

1. I open the Error.Blend file in Blender. The file contains a light bulb created by extruding and shaping a circle. It is thickened using Modifier, Generate, Solidify.

Error.blend.txt

2. When I try to export the file to FDS I receive the error "BMElemSeq[index]: outdated internal index table, run ensure_lookup_table() first"
3. If I select the object and modify it using Modifier, Generate, Subdivision Surface on the object I am able to export to FDS.

[phart1]

I did a bit more investigating. This may be due to a malformed geometry. In Blender I used the X-Ray feature and found some indication of defects.

I recreated the bulb using a coarser mesh and check it with X-Ray feature. All good. So far no errors. So I would not spend anytime on investigating this at this point.

[emanuelegissi]

Thank you Paul for the feedback. Anyway I am going to track the cause of the problem. It should not happen... "When old people used to wish each other peace, we didn't understand the meaning of this word. Now we really understand." [Natalia Balasynovych, mayor of Vasilkiv, Ukraine 2022] Il mar 10 giu 2025, 17:13 Paul Hart ***@***.***> ha scritto:

…

*phart1* left a comment (firetools/blenderfds#56) <#56 (comment)> I did a bit more investigating. This may be due to a malformed geometry. In Blender I used the X-Ray feature and found some indication of defects. I recreated the bulb using a coarser mesh and check it with X-Ray feature. All good. So far no errors. So I would not spend anytime on investigating this at this point. — Reply to this email directly, view it on GitHub <#56 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACXMVY5YQGMKJBSWFKHCRY33C3Y25AVCNFSM6AAAAAB6WSVIIWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDSNJZGY2DONRTGA> . You are receiving this because you commented.Message ID: ***@***.***>

[phart1]

I encountered the same error with the attached file. It consists of the objects. The error occurs when the objects are joined into one object and an export to FDS is attempted.

Cface.blend.txt

[phart1]

I ran into the error when troubleshooting intersecting GEOMs. I used mesh cleanup method "Split Non-Planar Faces" and it resolved the error and the file was exported.

[phart1]

Also solved the issue in another situation by using "Make Planar Faces".

[phart1]

I may have gotten lucky with the solutions above. After a lot of investigating I cannot pin down what causes it or how to solve it.

[emanuelegissi]

Thank you, Paul.