Not able to define Alphanumeric Internal Number Range for Material Type Group

Dear Friends,

I have created four material types which is to be assigned to a specific group, but when Defining Number Range for Each Material Type  , I create a new group by pressing "F6" .

I am facing issue in assigning number range in two ways -

1) When i am assigning Internal Number Range Only - as shown in attachment - I am getting error - " Enter Numeric Range Only" .

How can I enter a Alphanumeric Number Range for Internal Assignment

2) When i am assigning External Number Range only - as shown in attachment 0 I am getting error -  "Enter Intervals without Overlap".

But the esiting No range is of 8 Digits starting from "A" - "ZZZZZZZZ",  but my no range will start from 9 digits as shown, than also getting the same error". Also i have checked the ma length of material type. It is set to 18

Please help

Thanks In Advance

Himanshu