Megawizard plug-in manager error

Hi all

I installed QuartusII 8 SP1 on a Windows Vista home premium SP1 64bit edition. All works well except megawizard. When I try to put a new symbol from megafunctions into a block diagram file, megawizard starts correctly but the first time I press "next" I get the following error message: "Megawizard plug-in manager: no launch command line found for megafunction plugin <function name, e.g. LPM_MULT>".

Can anyone help me?

Thanks in advance

Mauro