I'm trying to hide the workbook that contains my macro library. This used to
work, but has suddenly failed in 2 ways: the line "wb.Visible = False"
produces the error "Object doesn't support this property or method" and the
error is not trapped.

Sub auto_open()

Dim i&, wb

For i& = 1 To Workbooks.Count
Set wb = Workbooks(i&)
If InStr(UCase$(wb.Name), "PERSONAL.XLS") Then GoSub HideWB
If InStr(UCase$(wb.Name), "CUSTOM.XLS") Then GoSub HideWB
Next i&

Exit Sub

HideWB:

On Error GoTo SkipHide
wb.Visible = False
SkipHide:
On Error GoTo 0
Return

End Sub

What could be going wrong?