VBA - Sheets.count - subscript out of range - vba

Question

Below is a macro which I wrote about three years ago, when I was a much less proficient VBA coder than I am today. There are a number of obvious things which I would simplify/do differently today. However, it is still in use and generally works. The manager of the relevant admin process copies and pastes this code into different workbooks every time we set up a new customer, and changes around a few of the variables. This has worked fine until today, when it has suddenly started generating a "subscript out of range" error when used in a new worksheet.
The error generates on the line workdaybook.Sheets("Sheet1").Copy salesBook.Worksheets(Sheets.Count). I have checked and "salesBook" has been defined. However, hovering the cursor over "salesBook.worksheets(Sheets.Count) brings up a "subscript out of range" message.
I know that overall, this code isn't the best-written in the world, but I am puzzled by it suddenly failing on this line, having worked previously for about three years when pasted into multiple different workbooks.
Option Explicit
Sub salescalc()
'Application.DisplayAlerts = False
'On Error GoTo Errorcatch
Application.ScreenUpdating = True
Dim salesBook As Workbook
Dim CurrentWeekSheet As Worksheet
Set salesBook = ThisWorkbook
Set CurrentWeekSheet = ThisWorkbook.ActiveSheet
Dim workday As Date
Dim nextworkday As Date
Dim workdaybook As Workbook
workday = InputBox("Insert date in format dd/mm/yy", "userdate")
nextworkday = workday + 1
'find bottom row of "table"
Dim bottomrow As Range
For x = 1 To 6500
If CurrentWeekSheet.Cells(x, 1).Interior.ColorIndex = 19 Then
coloured_row = Range("A" & x).Row
End If
Next x
Set bottomrow = Range("A" & coloured_row)
'finds beginning and end of day's range
Dim workdayrange As Range
Dim nRow As Long
Dim workday_date As Variant
Dim nStart As Long, nEnd As Long
' Work out where the range should start - works
For nRow = 1 To 65536 'change this to xldown
If CurrentWeekSheet.Range("A" & nRow).Value = workday Then
'nStart = nRow + 3
nStart = nRow + 1
Exit For
End If
Next nRow
' Work out where the range should end - works
For nRow = nStart To 65536
If CurrentWeekSheet.Range("A" & nRow).Value = nextworkday Or Range("A" & nRow).Row = bottomrow.Row Then
nEnd = nRow
Exit For
End If
Next nRow
'distinction between bottom row and next date - offset less for bottomrow
If nEnd = bottomrow.Row Then
nEnd = nEnd
Else
If nEnd <> bottomrow.Row Then
nEnd = nEnd - 2
End If
End If
Set workdayrange = CurrentWeekSheet.Range("F" & nStart & ":F" & nEnd)
workday_date = Format(workday, "dd-mm-yy")
'identify which month is referred to based on date input by user (workday_date)- this will need to be updated in 2016
If Year(workday_date) <> 2017 Then
MsgBox "Date must be in 2017. If you require info for another year, please contact xxxxx."
Exit Sub
Else
Workbooks.Open ("U:\\(Folder)\\(subfolder)\\(Subfolder)\\2017\\" & workday_date & ".xlsx")
Worksheets("Sheet1").Activate
End If
Set workdaybook = ActiveWorkbook
Dim workdaysheet As Worksheet
Set workdaysheet = ActiveSheet
workdaybook.Activate
workdaybook.Sheets("Sheet1").Copy salesBook.Worksheets(Sheets.Count)
ActiveSheet.Name = "salesdata"
Dim sheetforcopy As Worksheet
Set sheetforcopy = Sheets.Add
sheetforcopy.Name = "Sheetforcopy"
CurrentWeekSheet.Range("F" & nStart & ":F" & nEnd).EntireRow.Copy
sheetforcopy.Range("A185").PasteSpecial xlPasteValues
sheetforcopy.Range("F" & nStart & ":F" & nEnd).Formula = "=if(D185<>0,SUMIFS(salesdata!E:E,salesdata!B:B,""*""&D185&""*"",salesdata!B:B,""*Total*""),"""")"
sheetforcopy.Range("L" & nStart & ":L" & nEnd).Formula = "=IF(IF(ISNUMBER(B185)=TRUE,COUNTIF(salesdata!B:B,""*""&B185&""*"")-1,"""")=-1,0,IF(ISNUMBER(B185)=TRUE,COUNTIF(salesdata!B:B,""*""&B185&""*"")-1,""""))"
sheetforcopy.Range("F" & nStart & ":F" & nEnd).Copy
CurrentWeekSheet.Range("F" & nStart & ":F" & nEnd).PasteSpecial xlPasteValues
CurrentWeekSheet.Range("F" & nStart & ":F" & nEnd).Copy
CurrentWeekSheet.Range("F" & nStart & ":F" & nEnd).PasteSpecial xlPasteValues
sheetforcopy.Range("L" & nStart & ":L" & nEnd).Copy
CurrentWeekSheet.Range("L" & nStart & ":L" & nEnd).PasteSpecial xlPasteValues
CurrentWeekSheet.Range("L" & nStart & ":L" & nEnd).Copy
CurrentWeekSheet.Range("L" & nStart & ":L" & nEnd).PasteSpecial xlPasteValues
Application.DisplayAlerts = False
Worksheets("salesdata").Delete
Worksheets("sheetforcopy").Delete
Application.DisplayAlerts = True
workdaybook.Close
CurrentWeekSheet.Activate
CurrentWeekSheet.Range("F" & nStart).Select
Application.ScreenUpdating = True
Application.DisplayAlerts = True
Exit Sub
'Errorcatch: MsgBox "Error - (confidential message deleted)."
End Sub