Jolene,

You don't need to intialize x. The code below will do what you want.

For x= 1 to Alen(Afieldnames)
     CAField = "A." + Allt(Afieldnames[x])
     CBField = "B." + Allt(Afieldnames[x])
     If EVALUATE(CAField) != EVALUATE(CBField)
          Replace (CAField) with EVALUATE(CBField)
     Endif
Next