I have a lot of formulas in a sheet that look like this:

=INDIRECT("'" &"Summary by Unit & Class "&$AA$1 &"'!" &
columnletter(COLUMN(B47)) & ROW(C45)-1)

When I open the file, oftentimes these formulas have #Value in them. I just
hit F9 and it goes away. The calculation mode is automatic and I don't want
end users having to refresh to get rid of the errors in cells. Ideas?

Note: Columnletter is a UDF:

Function ColumnLetter(ByVal colNum As Long) As String
Do
ColumnLetter = Chr$(65 + (colNum - 1) Mod 26) & ColumnLetter
colNum = (colNum - 1) \ 26
Loop While colNum 0
End Function