The inp file exporter works well but there are issues with the importer:
What do you want to do with these ref points - use them for coupling constraints ? Then you can define such constraints using the Keyword Editor, without the need to export the inp file.
Even if inp file export is necessary for some reason (e.g. because keyword edits require modification of existing keywords which is not possible in GUI at the moment), it’s better to do it after setting everything else and then just run the analysis outside of PrePoMax using CalculiX executable. Then you can open the results file (.frd) in PrePoMax for postprocessing.