How to group by an aliased field?

Hi there

Why the following SQL clause is not working for the MS SQL 2012 (BTrieve is Ok with it):

select a, b, 'Hint: Processed '+a as Hint, Sum(s) from MyTable group by a, b, Hint

The error message is

If there any way not to make duplications like

select a, b, 'Hint: Processed '+a as Hint, Sum(s) from MyTable group by a, b,  'Hint: Processed '+a ?

Thanks.