Hi Thomas,
If you go to the User Files Folder > Themes > AnalysisAndReportTable, you can see a list of all the theme files. In that folder, you will probably find a file named "0-FitNL-voisins1.ois". Please try changing this filename to "voisins1.ois" or calling the theme using the "0-FitLinear-" prefix in your command using quotes:
nlbeginr irng:=2 theme:="0-FitNL-voisins1.ois"
Note that on my end, it currently still produces an error warning but the nlt tree object gets created properly. I will have a colleague look at the possible causes of the error message.
Let me know if this helps you get a step further in your code, and where your next roadblock occurs if any.
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Edit: To avoid an error, the .ois file must be moved to C:\Program Files\OriginLab\OriginXXXXX\Themes\AnalysisAndReportTable
but it does not need to be renamed (so filename 0-FitNL-voisins1.ois should allow it to be called simply as "voisins1" when using nlbeginr)
Best,
Nicholas G.
nicholas@originlab.com
OriginLab Technical Support Team