Unable to get my code to execute paste special - excel

Question

I have a small VBA code to copy a row from one sheet and paste to another, it works fine for paste but not for paste special, as I am trying to paste values only and not just paste.
this is my code, very basic. Noted that the pastespecial is changed to paste the code works fine.
thanks for you help
Private Sub CommandButton1_Click()
a = Worksheets("Inventory List Costing Review").Cells(Rows.Count, 1).End(xlUp).Row
For i = 10 To a
If Worksheets("Inventory List Costing Review").Cells(i, 19).Value = "Completed" Then
Worksheets("Inventory List Costing Review").Rows(i).Copy
Worksheets("Completed by Sales").Activate
b = Worksheets("Completed by Sales").Cells(Rows.Count, 1).End(xlUp).Row
Worksheets("Completed by Sales").Cells(b + 1, 1).Select
ActiveSheet.PasteSpecial Paste:=xlPasteValues, operation:=xlNone
Worksheets("Inventory List Costing Review").Activate
End If
Next
Application.CutCopyMode = False
ThisWorkbook.Worksheets("Inventory List Costing Review").Cells(1, 1).Select
End Sub

Answer 1

PasteSpecial xlPasteValues vs Assigning Values
A Quick Fix
If you insist on using PasteSpecial, in the IF clause you can use:
Worksheets("Inventory List Costing Review").Rows(i).Copy
b = Worksheets("Completed by Sales").Cells(Rows.Count, 1).End(xlUp).Row
Worksheets("Completed by Sales").Cells(b + 1, 1).PasteSpecial Paste:=xlPasteValues
But a better (more efficient) way is:
b = Worksheets("Completed by Sales").Cells(Rows.Count, 1).End(xlUp).Row
Worksheets("Completed by Sales").Rows(b + 1).Value = _
Worksheets("Inventory List Costing Review").Rows(i).Value
when Application.CutCopyMode = False and ... Cells(1, 1).Select are not needed anymore.
Improvements
If you use Option Explicit, it will 'force' you to qualify all variables (a, b).
If you additionally qualify the workbook and worksheets, the code becomes quite readable.
Since the code can be run from a command button on any sheet, you can give it a suitable name and put it into a standard module. Then you can easily call it in the click event code of a command button (located in a sheet module).
Standard Module e.g. Module1
Option Explicit
Sub updateSales()
Dim wb As Workbook
Set wb = ThisWorkbook ' The workbook containing this code.
Dim src As Worksheet
Set src = wb.Worksheets("Inventory List Costing Review")
Dim tgt As Worksheet
Set tgt = wb.Worksheets("Completed by Sales")
Dim a As Long
Dim b As Long
a = src.Cells(src.Rows.Count, 1).End(xlUp).Row
For i = 10 To a
If src.Cells(i, 19).Value = "Completed" Then
b = tgt.Cells(tgt.Rows.Count, 1).End(xlUp).Row
tgt.Rows(b + 1).Value = src.Rows(i).Value
End If
Next
End Sub
Sheet Module e.g. Inventory List Costing Review and/or Completed by Sales
Option Explicit
Private Sub CommandButton1_Click()
updateSales
End Sub

Answer 2

The following should work (cleaned up a bit of clutter along the way).
Although if you're just copying data from cells it would be faster to assign the values directly to the destination cells instead of copy-pasting.
Private Sub CommandButton1_Click()
With Worksheets("Inventory List Costing Review")
a = .Cells(Rows.Count, 1).End(xlUp).Row
For i = 10 To a
If .Cells(i, 19).Value = "Completed" Then
.Rows(i).Copy
b = Worksheets("Completed by Sales").Cells(Rows.Count, 1).End(xlUp).Row
Worksheets("Completed by Sales").Cells(b + 1, 1).PasteSpecial Paste:=xlPasteValues, operation:=xlNone
End If
Next
Application.CutCopyMode = False
.Cells(1, 1).Select
End With
End Sub