If anyone is interested, I have found a solution to the problem. It seems that the error was caused by a conflict with the Nvidia video driver for my video card. I uninstalled the driver in Device Manager, then install Goldwave, before re-installing the Nvidia drivers. Everything is now working as it should.
I still don't understand why the problem occured only after SP2 was installed. Maybe someone can figure that out.
All is well that ends well.