vba runtime error 1004 application defined or object defined error

Something very strange happened. At one point this was working and all of a sudden now I get an error. The issue is fm and sm, when the debug is on, fm = Empty and sm = Empty Therefore tval = Empty the error occurs at line 34 ; tval = WorksheetFunction.Sum(ws.Range(ws.Cells(fm, 11), ws.Cells(sm, 11)))

Private Sub TextBox6_Change()

Dim ws As Worksheet
Dim sr, leg, lr, fm, sm, tval, sval, i, j As Long       
Dim wo, rc As String

Set ws = ThisWorkbook.Worksheets("Cost Analysis")       ' ws = Work Sheet
sr = 5                                                  ' sr = Start row
lr = ws.Cells(Rows.Count, 1).End(xlUp).Row              ' lr = Last row
wo = Trim(UserForm1.TextBox4.Value)                     ' Work Order
leg = Trim(UserForm1.TextBox5.Value)                    ' leg
rc = Trim(UserForm1.ComboBox3.Value)                    ' rc = Root Cause

If wo <> "" And leg <> "" And rc <> "" And TextBox6.Value <> "" Then

If Application.WorksheetFunction.CountIfs(ws.Cells(sr, 1).Resize(lr, 1), wo, _
                                            ws.Cells(sr, 4).Resize(lr, 1), leg, _
                                            ws.Cells(sr, 5).Resize(lr, 1), rc) > 0 Then

        For i = sr To lr
                If Trim(ws.Cells(i, 1)) = wo And Trim(ws.Cells(i, 4)) = leg Then
                    j = j + 1
                        If j = 1 Then
                            fm = i
                        End If
                            If Trim(ws.Cells(i, 5)) = rc Then
                                    sm = i
                                    Exit For
                                          Else
                            End If
                End If
        Next

        tval = WorksheetFunction.Sum(ws.Range(ws.Cells(fm, 11), ws.Cells(sm, 11)))
        sval = WorksheetFunction.Sum(ws.Range(ws.Cells(fm, 11), ws.Cells(sm, 11))) * Trim(TextBox6.Value)

            Else
 End If
End If

UserForm1.TextBox7 = tval
UserForm1.TextBox16 = sval

End Sub