There is a E message when i am creat a Merchandise Categories by wg21, it is ：
No material type has been defined for MG materials
Message no. WW059
Define the attributes of the material type for the material group material in Customizing.
Select "1" as the ID for assignment of the material type to identifier in Customizing.
Make any necessary Customizing settings if you have the required authorization.
Contact your system administrator if you cannot make the settings yourself. Take into account the industry IMG and the retail IMG, since the material type identifier is only used in retail.
who can help me to solve it ?