only numerical number for roh material type

Hi,MM team

I have a small issue plz help me out

using oms2-i have copied material type-ROH to 1001,

later using mmnr- i have defined number range,

my requirement is for this material type 1001 i should give only numericals nd they are externaly feed,wheni enter in mm01 its throughing error saying for this material type u cannot define only numericals ,so plz team give what settings will help me to come out of this issue