The End statement should never be used, except for reasons really serious.

If your application stay in memory means that not all component are been properly released.
Paradoxically End may be the cause of the problem.

On the main form you should ensure to unload all forms, use a routine like this to release all forms:

Code:
Private Sub CloseAllForms()
    Dim f As Form
    For each f in Forms
         If f.Name <> Me.Name Then
             Unload f
        End If
    Next
End Sub