Sub Workbook_Open()
    Call SaveIt
End Sub

Option Explicit

Sub SaveIt()

Dim xWb As Workbook
Dim dt As String

Application.DisplayAlerts = False

dt = Format(CStr(Now), "yyyy_mm_dd_hh_mm_ss")

For Each xWb In Application.Workbooks

If xWb.Path = vbNullString And Not xWb.ReadOnly And Windows(xWb.Name).Visible Then
    xWb.SaveCopyAs Filename:="C:\User\Desktop\Excels" & "\" & dt & " - " & xWb.Name & ".xlsx"   ' __ ВОТ ЗДЕСЬ ОШИБКА __
Else
If Not xWb.ReadOnly And Windows(xWb.Name).Visible Then
    xWb.SaveCopyAs Filename:="C:\User\Desktop\Excels" & "\" & dt & " - " & xWb.Name
End If

End If

Next

Application.DisplayAlerts = True

Application.OnTime Now + TimeValue("00:05:00"), "SaveIt"

End Sub

Sub test() 
Dim c As Range 
For Each c In ActiveSheet.UsedRange.Cells 
If c.HasFormula Then
If InStr(1, c.Formula, "SUM") <> 0 Then c.Value = c.Value 
End If
Next
End Sub

Sub test() 
Dim c As Range 
For Each c In ActiveSheet.UsedRange.Cells 
If c.HasFormula Then 
If InStr(1, c.Formula, "SUM"   <> 0 Then c.Value = c.Value 
End If 
Next 
End Sub

Sub Поиск()
LastRow = Sheets("111").Range("B65536").End(xlUp).Row
Dim StringToFind As String
For i = 1 To LastRow
    StringToFind = Sheets("111").Range("B" & i).Value 'значение для поиска
    
        '<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>
        On Error GoTo 1
        Dim FirstFoundCell As Range, FoundCell As Range
        Application.ScreenUpdating = False
    
        Set FirstFoundCell = Range("C2:L2").Find(what:=StringToFind)
        FirstFoundCell.Offset(3, 0) = StringToFind
    
        If FirstFoundCell Is Nothing Then
            Exit Sub
        End If
    
        Set FoundCell = FirstFoundCell
        Do
            Set FoundCell = Range("C2:L2").FindNext(After:=FoundCell)
            FoundCell.Offset(3, 0).Value = StringToFind
            If FoundCell.Address = FirstFoundCell.Address Then Exit Do
        Loop
1:
Next i
End Sub

Private Sub Worksheet_Calculate()
Dim rWatchRange As Range
Dim sBook As String
Dim sFilePath As String

On Error Resume Next
Application.EnableEvents = False
Set rWatchRange = Range("B2:H2")

 If Intersect(ActiveCell, rWatchRange) Is Nothing Then
  Set rWatchRange = Nothing
    Exit Sub
 End If
 
sBook = ActiveCell
sFilePath = Range("FilePath")

 
 Application.DisplayAlerts = False
 
  ActiveCell.Offset(10, 0).Formula = _
    "='" & sFilePath & "[" & sBook & ".xls]Sheet1'!R1C1"
  
 Application.EnableEvents = True
 Application.DisplayAlerts = True
 On Error GoTo 0
End Sub