Where can I update quantity in material master ?

I was working on STO (Stock Tranport Orders) scenarios

Bascially stock tranport orders can be done in three ways

1. Stock Transport via stock transport procedure using 1 step procedure

2. Stock Tranport via stock tranport posting using 2 step procedure

3. Stock Tranport using a STO ( in Tcode me21n, where we select STO)

Now, when I entered MIGO and selected Transfer posting and movement type 301

(Transfer posting from plant to plant) and maintained the material details

It is throwing up a message "Shortfall of stock level"

I went to material master of the respective material for both the plants and updated the base quantity in the sales view ( base quantity field , under the shipping data ( times of day) block)

Yet, it did not fix my problem and I am not sure where else I can maintain <b>quantity in the material master for the material</b>Any inputs into the above will be helful

Thanks for your time