Because AttachPane can be called after form_load event.

if you need to access frmPropertyGrid in form_load you can use your code,

sub form_load()

load frmPropertyGrid

end sub

...

        Case ID_PANE_PROPERTIES:
               If Not frmPropertyGrid Is Nothing Then
                     Item.Handle = frmPropertyGrid.hwnd
               End If

Forms attached using the DockingPaneManager_AttachPane procudeure are not accessable.

Example:

             If frmPropertyGrid Is Nothing Then
                 Set frmPropertyGrid = New frmPropertyGrid
             End If
Now if you try to access the frmPropertyGrid variable in your forms, it will not be seen as if it is not loaded in VB, the only solution is to load the form and show it early in the program before the attach is reached then refernce to teh form direct not through a new variable:

sub form_load()

load frmPropertyGrid

end sub

        Case ID_PANE_PROPERTIES:
'              If frmPropertyGrid Is Nothing Then
'                  Set frmPropertyGrid = New frmPropertyGrid
'              End If
             Item.Handle = frmPropertyGrid.hwnd

Am I missing something