Valuation Class

Is it possible to assign various account category reference for one valuation class. When I try to do then system shows me error message that "An entry already exists with the same name " Message no. SV009.

The reason why I am doing this is for my new 7 material types out of 8 I have to use only one valuation class & for the last material type other valuation class. Please suggest how to do this.

Waiting for your suggestions.

Thanks,

Abhijit