Hi all, I have code (see below) in sheet module

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, Cancel
As Boolean)
If Not Application.Intersect(Range("D11:D12"), Target) Is Nothing Then
UserForm1.Show
End If
End Sub

when i double click on range D11 or D12 i get error message saying
" Run-time error '459':
Object or class does not support the set of events "

and when i click on debug then line "UserForm1.Show" gets higlighted.
It was working alright couple days ago but suddenly i start getting
this error. Please can any friend can help.