First:
Dim T(10) As FileSystemWatcher
The number of drives might more than that
Second:
T(N) is null or Nothing, new instance of FileSystemWatcher required
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim allDrives2() As IO.DriveInfo = IO.DriveInfo.GetDrives()
Dim N As Integer = 0
Dim T(allDrives2.Length - 1) As IO.FileSystemWatcher
For Each dd As IO.DriveInfo In allDrives2
If dd.IsReady = True Then
T(N) = New IO.FileSystemWatcher
T(N).Path = dd.Name
T(N).IncludeSubdirectories = True
T(N).EnableRaisingEvents = True
N += 1
End If
Next
End Sub