@TIG Thank you for your input. My understanding of the C SDK is: SUModelSaveToFileWithVersion(model, "SU2021.skp", SUModelVersion_SU2021); - Should save into the "versionless" 2021 format and it should load without any error or warning into SU 2022 and SU 2023 SUModelSaveToFileWithVersion(model, "SUcurrent.skp", SUModelVersion_Current); - should save in the version of the SDK (in this case 2024) But instead both function calls save in SU 2024 format which IMO is an error in the SDK. I'll try to contact them to sort this.

And it works flawless with v2015 files. Thanks again.

Thank you for checking it.

Thank you AdamB. I did add the path of the downloaded .dll and .lib to the VS library search path. Somewhere I read that character encoding differences could cause such error messages. So I also tried to change the project's encoding settings without any luck.... EDIT: Thank you. SUCCESS!!! (Well it was a missing reference to the lib... )