I have to run my code several times for it to execute entirely - excel

Question

I'm not sure whether it's because I'm using a mac or the code is wrong, but the rows aren't identifying properly, and therefore not deleting or pasting it into the other spreadsheet. I have to run the code three times for it to properly go through it and copy/paste and delete the cells into the other spreadsheet.
Many thanks!
here is the code:
Dim j, lastidno As Long
Sheets("Part B + C Modules").Activate
lastidno = Range("A2", Range("A2").End(xlDown)).Count + 1
For j = 2 To lastidno
If Range("O" & j) = "" Then
Sheets("Part B + C Modules").Range("A" & j).Copy
Sheets("No Options Selected").Select
NextRow = Cells(Rows.Count, 1).End(xlUp).Row + 1
Cells(NextRow, 1).Select
ActiveSheet.Paste
Sheets("Part B + C Modules").Activate
Rows(j).EntireRow.Delete
End If
Next
MsgBox "done"
End Sub

Answer 1

Iteration and deleting rows goes backwards using a negative Step > For j = lastidno to 2 Step -1
However, it appears you could rewrite your code a bit more elegantly to avoid:
Implicit Range references
Iteration
Use of Activate or Select
The key is to have Explicit sheet references to work with. Also the use of SpecialCells can come in handy here to return a Range in one go (so no more iteration). This way you can also delete all rows in one go!
You code could, for example, look like:
Sub Test()
'Set up your worksheet variables
Dim ws1 As Worksheet: Set ws1 = Worksheets("Part B + C Modules")
Dim ws2 As Worksheet: Set ws2 = Worksheets("No Options Selected")
'Get last used rows
Dim lr1 As Long: lr1 = ws1.Cells(ws1.Rows.Count, 1).End(xlUp).Row
Dim lr2 As Long: lr2 = ws2.Cells(ws2.Rows.Count, 1).End(xlUp).Row
'Set your range and copy it
Dim rng As Range: Set rng = ws1.Range("O2:O" & lr1).SpecialCells(xlCellTypeBlanks).Offset(0, -14)
rng.Copy ws2.Cells(lr2 + 1, 1)
'Delete your range
rng.EntireRow.Delete
MsgBox "done"
End Sub
Small catch: SpecialCells will return an error when no empty cells are found. You might want to work your way around that using On error or count the empty cells in your Range first (my personal preference). So that specific part could looke like:
'Set your range and copy it
If WorksheetFunction.CountBlank(ws1.Range("O2:O" & lr1)) > 0 Then
Dim rng As Range: Set rng = ws1.Range("O2:O" & lr1).SpecialCells(xlCellTypeBlanks).Offset(0, -14)
rng.Copy ws2.Cells(lr2 + 1, 1)
End If
Another small note for future reference: Dim j, lastidno As Long only has lastidno declared as Long data type. j Variable is auto-assigned to Variant/Integer so could potentially become a problem when your data is larger than this data type can hold > Return an OverFlow error.