ActiveStepIndex debe ser menor que WizardSteps.Count y ser al menos -1. Para pasos agregados dinámicamente, asegúrese de que se agregan antes del evento Page_PreInit o en el mismo.
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English version
The ActiveStepIndex must be less than WizardSteps.Count and at least -1. For dynamically added steps, make sure they are added before or in Page_PreInit event.
.Net Framework