On Error

[gavio]

You can use something like this (write in Append mode so you don't loose previous entries):

Option Explicit
 
Private Sub Form_Load()
On Error GoTo ErrorHandeler
    Debug.Print 1 / 0
        Exit Sub
ErrorHandeler:
    writeLog Err.number, Err.description, "Form1 Form_Load"
End Sub
 
'in module
Public Sub writeLog(number As Long, description As String, procedure As String)
    Dim ff As Integer: ff = FreeFile
        Open App.Path & "\error.log" For Append As #ff
            Print #ff, Format(Date, "dd.mm.yy") & ", " & Format(Time, "hh:mm:ss") & " - error #" & number & " - " & description & " - " & "in " & procedure & " procedure"
        Close #ff
End Sub