"Do...Until" problem (Error 1004)

Hi.

I'm trying to find the Cell that contains the string "Grand Total" along row 5.
The following code is giving me Error 1004

Dim column As Long
column = 1
Do Until ActiveWorkbook.ActiveSheet.Cells(5, column) = "Grand Total"
column = column + 1
Loop

The "Do Until ActiveWorkbook.Activ...." line is highlighted in Debugger as the problem line.

Any ideas?