Typically, your object should have "BaseEntity" as it's parent. When BaseEntity is selected as the parent, it will inherit an Id column (plus others) and the Id column will be selected as the Id column for the object. The error is letting you know that the object does not have a column selected as the Id column (when you select BaseEntity as the parent it will select the Id column as the objects "Id" property).
Typically, your object should have "BaseEntity" as it's parent. When BaseEntity is selected as the parent, it will inherit an Id column (plus others) and the Id column will be selected as the Id column for the object. The error is letting you know that the object does not have a column selected as the Id column (when you select BaseEntity as the parent it will select the Id column as the objects "Id" property).