cannot retrieve column titles from another workbook - excel

Question

I am trying to copy the string values(column titles) from another workbook in row 4 as captions for checkboxes in the workbook where I am running the code. This is what I have so far and it is not working because it is showing the error message "Subscript out of range, run time error 9" Here is what I have. After the error message pops up the line marked below is highlighted. Can anybody help me please. Thank you very much.
Function CallFunction(SheetName As Variant) As Long
Dim text As String
Dim titles(200) As String ' Dim titles(200) As String ' Array
Dim nTitles As Integer
Dim wks As Worksheet
Dim myCaption As String
PathName = Range("F22").Value
Filename = Range("F23").Value
TabName = Range("F24").Value
ControlFile = ActiveWorkbook.Name
Workbooks.Open Filename:=PathName & "\" & Filename
ActiveSheet.Name = TabName
Set wks = Workbooks("Filename").Worksheets(SheetName).Activate ' <= Highlights this line ****
For i = 1 To 199
If Trim(wks.Cells(4, i).Value) = "" Then
nTitles = i - 1
Exit For
End If
titles(i - 1) = wks.Cells(4, i).Value
Next
i = 1
For Each cell In Range(Sheets("Sheet1").Cells(4, 1), Sheets("Sheet1").Cells(4, 1 + nTitles))
myCaption = Sheets("Sheet1").Cells(4, i).Value
With Sheets("Sheet1").checkBoxes.Add(cell.Left, _
cell.Top, cell.Width, cell.Height)
.Interior.ColorIndex = 12
.Caption = myCaption
.Characters.text = myCaption
.Border.Weight = xlThin
.Name = myCaption
End With
i = i + 1
Next
End Function

Answer 1

Subscript out-of-range typically indicates that a specified Worksheet does not exist in the workbooks Worksheets collection.
Otherwise, are you sure that the workbook specified by FileName is already open? If not, that will raise the same error.
Ensure that A) the file is already open (or use the Workbooks.Open method to open it), and B) ensure that such a worksheet already exists (if not, you will need to create it before you can reference it by name).
Update
You have Workbooks("FileName") where "Filename" is a string literal. Try changing it to simply Filename (without the quotation marks) (this seems like the OBVIOUS error).
Also worth checking:
I also observe this line:
ActiveSheet.Name = TabName
If the sheet named by SheetName is active when the workbook opens, then that line will effectively rename it, so you will not be able to refer to it by SheetName, but instead you would have to refer to it by Worksheets(TabName). ALternatively, flip the two lines so that you activate prior to renaming:
Set wks = Workbooks(Filename).Worksheets(SheetName).Activate
ActiveSheet.Name = TabName
For further reading: avoid using Activate/Select methods, they are confusing and make your code harder to interpret and maintain:
How to avoid using Select in Excel VBA macros
If that is the case, then you could do simply:
Workbooks(Filename).Worksheets(SheetName).Name = TabName