Diagnosis
You are entering user-specific settings for BOM maintenance.
You entered &V1& as a default item category for class items. However,this item category is not for class items.

Procedure
Please display a list of the item categories defined in your company.To do this, look under the settings in Customizing (Bills of material)Item data -> Item categories.
For class items, you can only use an item category which contains theclass item indicator.