Clipboard exception on open

(Win XP SP2, Delphi 2007)

I'm getting this exception when I have a Notepad text file open, press Ctrl/C and then in another application try to paste.

if not OpenClipboard(FClipboardWindow) then
raise Exception.CreateRes(@SCannotOpenClipboard);

The call to the Clipboard comes in the Mask unit, WMPaste procedure:
...
Clipboard.Open;
Value := Clipboard.AsText;
Clipboard.Close;
...

The fault seems not to happen if I first close the Notepad text file. Could it be that Notepad is badly behaved?

Mike