I think I had the same problem as you and he posted the same error message.
Erreur lors de l'importation de l'entretien avec des questions d'identification 1, 1. EnquêteurId , QuestionnaireId 68fa82cb1fb845278ef19f47b2b92cc2$2, Exception: Index must be within the bounds of the List. Parameter name: index
You are either preloading a roster element for which the trigger question does not allocate capacity or preloading a roster with duplicates.
Sure, if you have a question, I can try to answer. For preloading functionality watch and do step-by-step this tutorial:
In addition to the abovementioned video tutorial this page will help troubleshoot user problems with preparing data files for Survey Solutions: