Global Settings for US - Unable to update Input Tax

Hi,

I need to update tax code in expense type master data for US expense types.. But the tax code field is not visible in the screen, because in the global settings for US(10), No Input Tax is selected.

Now I want to check the radio button Input Tax per Travel Expense Type and upate tax code in expense types for US.

But the tab strip Input Tax is greyed out and i am unable to select the radio button. However I am able to change for other countries like GB, DE etc..

Any help on this is much appreciated..

Thanks,

Praisty