Unpredictable errors VBA microsoft word copying comments and text to excel - excel

Question

I tried to make a macro that takes all the comments in a word document, filters based on the comment text and then inserts them in excel with the associated text in a note.
I tried each step iteratively and I managed to copy the comments and pasting the wanted results in the same word document. Then I managed to manipulate excel by adding columns and notes.
Everything broke when I integrated the excel part with the comment extraction part. The errors were invalid procedure call for the line with rightParPos = InStr(leftParPos, comment, ")") which I hadn't touched in a while, so I tried outputting the parameters... That lead to a completely different error - an indexing error for the categories array when categoryCount was 0, which also was very strange. After that I tried removing a strange character in a string and then I suddenly got some kind of "can't connect to excel" at Set xlWB = xlApp.Workbooks.Open(FileName:=xlPath).
It seems completely random to me. I'm thinking that it might be some kind of limit or bug in the Microsoft Word environment that is causing these problems. Anyone knowing what could be a cause of these strange errors?
I couldn't find anything out of the ordinary with my code, but maybe someone on S.O. sees something that immediately looks strange. Sorry for the very messy code.
Sub Test()
Dim comment, text As String
Dim pageNr As Integer
Dim codePrefix, fileName As String
Dim newLinePos, leftParPos, rightParPos As Integer
Dim commentNr As Integer
Dim codeWorksheetIndex As Integer
Dim xlFile, xlDir, xlPath As String
'Excel'
Dim xlApp As Object
Dim xlWB As Object
On Error Resume Next
Set xlApp = GetObject(, "Excel.Application")
If Err Then
Set xlApp = CreateObject("Excel.Application")
End If
On Error GoTo 0
xlFile = "TEST"
xlDir = "My\Directory\path\" 'censored
xlPath = xlDir & xlFile
Set xlWB = xlApp.Workbooks.Open(FileName:=xlPath)
codePrefix = "a-code" 'censored
fileName = Left(ActiveDocument.Name, Len(ActiveDocument.Name)-5)
'insert a column as second column in each spreadsheet'
For sheet_index = 1 to 3
With xlWB.Worksheets(sheet_index)
.Range("B:B").Insert
.Cells(1, 2).Formula = fileName
End With
Next sheet_index
For commentNr = 1 To ActiveDocument.Comments.Count
Dim category As String
Dim categories(1 to 2) As String
Dim categoryCount As Integer
Dim numLeft, numRight as Integer
'Dim j As Integer
comment = LCase(ActiveDocument.Comments(commentNr).Range)
text = ActiveDocument.Comments(commentNr).Scope
pageNr = ActiveDocument.Comments(commentNr).Scope.Information(wdActiveEndPageNumber)
'find newline'
newLinePos = InStr(comment, vbCr)
If newLinePos = 0 Then
newLinePos = InStr(comment, vbLf)
If newLinePos = 0 Then
newLinePos = InStr(comment, vbCrLf)
if newLinePos = 0 then
newLinePos = InStr(comment, Chr(10))
if newLinePos = 0 then
ActiveDocument.Content.InsertAfter Text:="ERROR: comment " & commentNr & " misses newline!" & vbNewLine
End If
End If
End If
End If
'set to initial index for leftpar instr'
rightParPos = 1
categoryCount = 0
Do
leftParPos = InStr(rightParPos, comment, "(")
rightParPos = InStr(leftParPos, comment, ")")
If leftParPos > 0 and rightParPos > 0 Then
numLeft = rightParPos-1
numRight = numLeft - leftParPos
category = Trim(Right(Left(comment, numLeft), numRight))
categories(categoryCount) = category
categoryCount = categoryCount + 1
End If
Loop While leftParPos > 0 And rightParPos > 0
comment = fileName & " (s. " & pageNr & ")" & vbNewLine & Trim(Right(comment, Len(comment)-newLinePos))
If Instr(LCase(comment), codePrefix) = 1 Then
For categoryIndex = 0 To categoryCount-1
category = categories(categoryIndex)
If category = "category1" Then
codeWorksheetIndex = 1
ElseIf category = "category2" Then
codeWorksheetIndex = 2
ElseIf category = "category3" Then
codeWorksheetIndex = 3
End If
With xlWB.Worksheets(codeWorksheetIndex)
.Cells(commentNr+1, 2).Formula = text
.Cells(commentNr+1, 2).NoteText comment 'this only worked without =
End With
Next categoryIndex
End If
Next commentNr
End Sub

Answer 1

There are two critical problems with the code that were overlooked and then there was one third problem that wasn't due to the code but which also resulted in errors.
As #TimWilliams mentioned, one case where leftParPos = 0 was unhandled.
The indexing of categories was entirely wrong and faulty in the code.
The strangest error was due to having the excel file on an external harddrive that disconnected and therefore making excel not responding.