If Schleife bei Fehler 13 worksheet in MsgBox

Private Sub Workbook_Open()
Call Startseite_Übersicht
Call Import_Data(Sheets("Entnahme"))
End Sub

Public Sub Import_Data(wks As Worksheet)
Dim objFileSearch As clsFileSearch
Dim lngIndex As Long, lngCount As Long
Dim varOutput As Variant
Dim strPath As String, strFormula As String
Const cstrTabname As String = "Report" 'Tabellenname
With wks
If .Range("C7") = "" Or .Range("C8") = "" Then
MsgBox ("Bitte Cellen C7 & C8 mit Daten füllen.")
Else
strPath = _
"I:\Partikelfallen\" & .Cells(7, 3).Value & "\" & .Cells(8, 3).Value & "\"  ' _
Startverzeichnis
If Right(strPath, 1)  "\" Then strPath = strPath & "\"
.Range("B17:C36").ClearContents
Set objFileSearch = New clsFileSearch
With objFileSearch
.NewSearch = True
.CaseSenstiv = False
.Extension = "*.xlsx*"
.FolderPath = strPath
.SearchLike = "*Partikelfallenanalyse_" & wks.Name & "_*"
.SubFolders = False
If .Execute(Sort_by_Date_Create, Sort_Order_Descending) > 0 Then
ReDim varOutput(1 To 20, 1 To 10)
lngCount = 1
For lngIndex = 1 To .FileCount
If lngCount > 20 Then Exit For
strFormula = "='" & .Files(lngIndex).FI_FolderPath
strFormula = strFormula & "[" & .Files(lngIndex).FI_FileName & "]"
strFormula = strFormula & cstrTabname & "'!"
varOutput(lngCount, 1) = strFormula & "U50"
varOutput(lngCount, 2) = strFormula & "I19"
varOutput(lngCount, 3) = strFormula & "I20"
varOutput(lngCount, 4) = strFormula & "I21"
varOutput(lngCount, 5) = strFormula & "I22"
varOutput(lngCount, 6) = strFormula & "I23"
varOutput(lngCount, 7) = strFormula & "I24"
varOutput(lngCount, 8) = strFormula & "I25"
varOutput(lngCount, 9) = strFormula & "I26"
varOutput(lngCount, 10) = strFormula & "U46"
lngCount = lngCount + 1
Next
End If
End With
With .Range("B17").Resize(UBound(varOutput, 1), 10)
.Formula = varOutput
.Value = .Value
End With
Set objFileSearch = Nothing
End If
End With
End Sub