VBA - Random Errors when saving multiple workbooks from a loop

[BigShango]

I'm at a loss with this one. I have a piece of code running down a list of names and saving a new workbook, with some info, for each name. It appears to fail randomly when trying to save. Like, 1st try it will fail at line 21 so I'll restart it from line 21 and it will run fine until say line 52. Next try (with no changes to the code) it will run until line 33 etc. It always fails on saving the workbook.

I've included the full code other than the save filepath as it had personal info in it.

Sub CreateBooks()

Set MB = Workbooks(ActiveWorkbook.Name)
Set M = MB.Sheets("Managers")
Set A = MB.Sheets("Sheet1")


For MRow = 1 To M.Range("A" & M.Rows.Count).End(xlUp).Row
    
    Manager = Trim(M.Range("A" & MRow).Value) & " " & Trim(M.Range("B" & MRow).Value)
    MB.Sheets("Awaiting Sign-Off").Copy
    Set NB = Workbooks(ActiveWorkbook.Name)
    Set N = NB.Sheets("Awaiting Sign-Off")
    
    For ARow = 2 To A.Range("A" & A.Rows.Count).End(xlUp).Row
                    
        If LCase(Trim(A.Range("D" & ARow).Value) & " " & Trim(A.Range("E" & ARow).Value)) = LCase(Manager) Then
            PasteRow = N.Range("A" & N.Rows.Count).End(xlUp).Offset(1).Row
            N.Range("A" & PasteRow).Value = A.Range("A" & ARow).Value
            N.Range("B" & PasteRow).Value = A.Range("B" & ARow).Value
            N.Range("C" & PasteRow).Value = A.Range("H" & ARow).Value
        End If
        
    Next ARow


    NB.SaveAs Filename:="R:\x" & Manager & ".xlsx", FileFormat:=xlOpenXMLWorkbook
    NB.Close Savechanges = True
    
Next MRow


End Sub

Any idea why this fails at random lines? The error is 'SaveAs method of workbook class failed'. It got all the way to line 61 before giving an error on the latest run. The folder that it is saving to is completely empty and there are no duplicate names listed.

Thanks