topic Custom objects become invalid when downgraded from AC29 to 27 in Libraries & objects

Custom objects become invalid when downgraded from AC29 to 27

Stefan Videnov — Wed, 09 Sep 2026 08:05:51 GMT

Hallo,

I've made a few custom objects with some relatively basic script. I need to access these objects with projects which are astill on archicad 27.
When I save our 29 template file to 28 and then 27 the objects unfortunately stop working. I do get the following error:

I haven't put anything into the "Forward migration" and "Background migration" fields, and tbh. I don't know how they are used.

Could you help me with moving the objects from 29 to 27?
Thank you!

Operating system used: Windows 11

Re: Custom objects become invalid when downgraded from AC29 to 27

CosminF — Wed, 09 Sep 2026 08:10:54 GMT

Hi,

maybe you'd want to look into this tool:
https://community.graphisoft.com/t5/GDL/Free-open-source-tool-downgrade-GDL-objects-gsm-to-older/m-p/706924#M8565

Re: Custom objects become invalid when downgraded from AC29 to 27

Barry Kelly — Wed, 09 Sep 2026 08:39:57 GMT

Do those objects call any macros from the 29 library?

If so that would be a possible cause for errors.

If they are "simple" objects with no macro calls, then I would have thought that they would have saved back.

But maybe there is an actual block that prevents 28 objects being saved back to 27.

Otherwise it might be possible to use the LP_XMLConverter - which sounds like the link CosminF gave does something similar.

Absolute worst case scenario, you could create a new object in 27 and re-create the parameters, and then copy and paste the script text.

Note that this will create a new object with a new GUID, so they will work in 27 and up into 28 and 29 but they will not be the same object as those you already have in 28 and 29.

They will be regarded as 2 separate objects.

I still create all of my objects in 25 so they will be compatible in all versions 25+.

Barry.