This has been reported and it seems to be the hardware that Windows has been installed upon. In the reported case the hardware was Intel based hardware for Apple Computer, Inc. with Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.080814-1236) installed on it.
We did not test the SSIM 4.6 or earlier UI installations for compatibility with Intel based hardware for Apple Computers and at this time you will be able to launch the SSIM UI using ssim40.jar file if you are using this hardware.