Ok you lot will be the only ones who will understand the fact that I cracked it with this:

RIGHT("0" + (DT_STR, 4, 1252) DATEPART("yyyy" , DATEADD("dd",-1,GETDATE())), 4) + "-" +

RIGHT("0" + (DT_STR, 2, 1252) DATEPART("mm" , DATEADD("dd",-1,GETDATE())), 2) + "-" +

"01"

Thanks for your help, as it did help.