USB Activity LED is flashing after starting the windows software. LED is always off when using the Linux software on OS X.
By the way: Strange behavior on one of my windows XP laptops: When opening the configuration dialog, the status constantly changes from "Emulator not detected!" to "Emulator ready!" and back. (About every second). Access to virtual floppy is not possible, USB LED is flashing as usual.
I'm now trying to compile the linux software on a real linux system. Maybe it's easier than trying to make it work on the Mac?!?
Edit: Success! The software works on Linux. So it must be a Mac OS X specific problem.