Error With WorksheetFunction Sum

[Ark68]

What could be causing an "Unable to get the Sum property of the WorksheetFunction class" error with this line in red?

        eqt_stcol = .Rows(2).Find(What:=UserForm1.uf1cbx2_eqt.Value, LookIn:=xlValues, LookAt:=xlWhole, MatchCase:=False).Column
        etotal_col = .Rows(2).Find(What:="ETOTAL", LookIn:=xlValues, LookAt:=xlWhole, MatchCase:=False).Column
        pstuse = .Cells(trow, eqt_stcol)
        .Cells(trow, eqt_stcol) = pstuse + stuse
        .Cells(trow, etotal_col) = WorksheetFunction.Sum(.Range("AT" & trow) & ":" & .Cells(trow, etotal_col - 1))

 

[Kenneth Hobson]

.Cells(trow, etotal_col) = WorksheetFunction.Sum(Range( _
  .Range(.Range("AT" & trow), .Cells(trow, etotal_col - 1))))

 

[Ark68]

Thank you Kenneth.