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• vbNullString is a remnant of VB6 (which I think would be under the Microsoft.VisualBasic.Constants namespace), and used to be a null string pointer often confused with "", an empty string. In VB.NET vbNullString is Nothing, so when you do this:

   If targetFolder = vbNullString Then
  

You're actually verifying whether targetFolder contains a reference at all... but you probably mean to check whether the provided string is null or empty. A more idiomatic way to test for this is String.IsNullOrEmpty:

    If String.IsNullOrEmpty(targetFolder) Then

• The following only apply if your project defaults options aren't customized:

• You're not specifying Option Explicit explicitly, but that's fine because in VB.NET that's the default behavior, contrary to VB6/VBA where implicit declarations are allowed by default.

• You're not specifying Option Strict either, and that's less fine, because by default, the VB.NET compiler won't enforce strict data typing - VB6/VBA was very loose with type conversions, and without Option Strict, VB.NET keeps a lot of that looseness. Note that Option Strict implies Option Explicit, so you don't have to specify both.

• You're specifying Imports statements, but then you fully-qualify things in these imported namespaces - this defeats the purpose: either you Imports namespaces, or you fully-qualify stuff. For example, you have Imports System.IO, so this code:

   files = System.IO.Directory.GetFiles(System.IO.Directory.GetCurrentDirectory(), "Export*.xlsx")
  

• vbNullString is a remnant of VB6 (which I think would be under the Microsoft.VisualBasic.Constants namespace), and used to be a null string pointer often confused with "", an empty string. In VB.NET vbNullString is Nothing, so when you do this:

   If targetFolder = vbNullString Then
  

    If String.IsNullOrEmpty(targetFolder) Then

• You're specifying Imports statements, but then you fully-qualify things in these imported namespaces - this defeats the purpose: either you Imports namespaces, or you fully-qualify stuff. For example, you have Imports System.IO, so this code:

   files = System.IO.Directory.GetFiles(System.IO.Directory.GetCurrentDirectory(), "Export*.xlsx")
  

• vbNullString is a remnant of VB6 (which I think would be under the Microsoft.VisualBasic.Constants namespace), and used to be a null string pointer often confused with "", an empty string. In VB.NET vbNullString is Nothing, so when you do this:

   If targetFolder = vbNullString Then
  

• vbNullString is a remnant of VB6 (which I think would be under the Microsoft.VisualBasic.Constants namespace), and used to be a null string pointer often confused with "", an empty string. In VB.NET vbNullString is Nothing, so when you do this:

   If targetFolder = vbNullString Then