Zipping a large folder fails

I am trying to archive logs to capture an intermittent fault where my logs are regularly overwritten. I wish to archive the logs to ensure I capture the required event.

I have written what appears to be funcional code to perform this, however if the folder is very large, the zip fails. If I point it to a smaller directory, it works without issue. There is no error generated, and I would appreciate any assistance in identifying the cause.

As I have never programmed in VBS before, I apologise in advance if this seems a simple question.

Option Explicit 
dim objFSO, objFolder, FolderToZip, ziptoFile 
dim ShellApp, eFile, oNewZip, strZipHeader 
dim ZipName, Folder, i, Zip 
Set objFSO = CreateObject("Scripting.FileSystemObject") 
Set objFolder = objFSO.GetFolder("D:\Program Files\afolder") 


Wscript.Sleep 2000 
Set oNewZip = objFSO.OpenTextFile("C:\Archive\logs_" & day(date) & month(Date) & Year(date)& ".zip", 8, True) 
strZipHeader = "PK" & Chr(5) & Chr(6) 
For i = 0 to 17 
 strZipHeader = strZipHeader & Chr(0) 
Next 
oNewZip.Write strZipHeader 
oNewZip.Close 
Set oNewZip = Nothing 
WScript.Sleep 5000 

FolderToZip = "D:\Program Files\afolder" 
ZipToFile = "C:\Archive\logs_" & day(date) & month(Date) & Year(date)& ".zip"
Set ShellApp = CreateObject("Shell.Application") 
Set Zip= ShellApp.NameSpace(ZipToFile) 
Set Folder= ShellApp.NameSpace(FolderToZip) 
Zip.CopyHere(FolderToZip) 
WScript.Sleep 2000

Your code is a little more complicated than it needs to be, but it works in principle. What's causing the failures you're experiencing with large folders is the fixed 2 second delay at the end:

WScript.Sleep 2000

CopyHere runs asynchronously, meaning that it runs in the background while the script continues. However, after 2 seconds delay the script terminates (and the Shell.Application instance with it), whether CopyHere has finished or not. When you have numerous/large files the processing may well take more than 2 seconds.

That's why your script works fine for small folders, but not for large ones. The copying simply isn't finished when the script terminates after 2 seconds.

To avoid this, replace the fixed delay with a check that compares the number of processed files to the total file count:

Set fso = CreateObject("Scripting.FileSystemObject")
Set app = CreateObject("Shell.Application")

zipfile = "C:\Temp\logs_" & Day(Date) & Month(Date) & Year(Date) & ".zip"
fldr    = "C:\Temp\sample"
cnt     = fso.GetFolder(fldr).Files.Count

'create a new empty zip file
fso.OpenTextFile(zipfile, 2, True).Write "PK" & Chr(5) & Chr(6) _
  & String(18, Chr(0))

'start copying the files from the source folder to the zip file
Set zip = app.NameSpace(zipfile)
zip.CopyHere app.NameSpace(fldr).Items     '<- runs asynchronously!

'wait for CopyHere to finish
Do
  WScript.Sleep 100
Loop Until zip.Items.Count = cnt