Log File

Depending on the amount of functionality you may want to create a simple log file.
One way of implementing this is to use a generic error handling routine in conjunction with a text file.
At the top of every subroutine and function add the following two lines of code:

Const sProcName As String = "MySubroutine" 
   On Error GoTo ErrorHandler 

At the bottom of every subroutine and function add the following lines of code:

   Exit Sub / Exit Function 
ErrorHandler: 
   Call Error_Handle(sProcName, Err.Number, Err.Description) 
End Sub / End Function 

Generic Error Handling Subroutine

Add the following subroutine to your project:

Public Sub Error_Handle(ByVal sRoutineName As String, _ 
                        ByVal sErrorNo As String, _ 
                        ByVal sErrorDescription As String) 
Dim sMessage As String 
   sMessage = sErrorNo & " - " & sErrorDescription 
   Call MsgBox(sMessage, vbCritical, sRoutineName & " - Error") 
   Call LogFile_WriteError(sRoutineName, sMessage) 
End Sub 

Using the Scripting Runtime Library

Add the following reference to your project Microsoft Scripting Runtime.

This reference is required if you want to use the File System Object library.

Add the following two global variables to your project.

Public g_objFSO As Scripting.FileSystemObject 
Public g_scrText As Scripting.TextStream 

Writing to the Log File

Add the following function to your project:

Public Function LogFile_WriteError(ByVal sRoutineName As String, _ 
                                   ByVal sMessage As String) 
Dim sText As String 
   On Error GoTo ErrorHandler 
   If (g_objFSO Is Nothing) Then 
      Set g_objFSO = New FileSystemObject 
   End If 
   If (g_scrText Is Nothing) Then 
      If (g_objFSO.FileExists("C:\temp\mylog.txt") = False) Then 
         Set g_scrText = g_objFSO.OpenTextFile("C:\temp\mylog.txt", IOMode.ForWriting, True) 
      Else 
         Set g_scrText = g_objFSO.OpenTextFile("C:\temp\mylog.txt", IOMode.ForAppending) 
      End If 
   End If 
   sText = sText & "" & vbCrLf 
   sText = sText & Format(Date, "dd MMM yyyy") & "-" & Time() & vbCrLf 
   sText = sText & " " & sRoutineName & vbCrLf 
   sText = sText & " " & sMessage & vbCrLf 
   g_scrText.WriteLine sText 
   g_scrText.Close 
   Set g_scrText = Nothing 
   Exit Function 
ErrorHandler: 
   Set g_scrText = Nothing 
   Call MsgBox("Unable to write to log file", vbCritical, "LogFile_WriteError") 
End Function