I had the same problem when I just upgraded to Snow Leopard. Found a work-around, but it it quite cumbersome, so it would be nice a more long-term solution. After all, the product was marketed as working for both Mac and Windows computers.
The problem seems to be isolated to the Secure Disk Tool application, which needs to be installed on the Mac, to be able to write a password to access the HD. No installation seems to be needed on Windows, where it just pops up.
When I upgraded to Snow Leopard, I also bought Windows 7. I installed it using VirtualBox - which can be downloaded for free at http://www.virtualbox.org/wiki/Downloads - so that I can run it side-by-side with Snow Leopard.
When Windows 7 is turned on, you plug in the external harddrive, and you will be asked for a password to access the harddrive. Type in the password. You will now gain access to the harddrive in the Windows virtual environment - but the hard disk will not appear in Snow Leopard, because only one of the operating systems will have access to the hard drive at any one time. You could now copy your files to a shared folder, and get them over to Snow Leopard. However, that would change all the creation dates of the folders, and I also encountered some errors when copying files with long names. Instead, shut down Windows 7. When Windows 7 relinquishes the hard drive, it pops up under Snow Leopard. Because the password was entered in Windows 7, there is no need to type a password, so the Secure Disk Tool application isn't needed.
This should work under any version of Windows, although I haven't tested it. So if there is so crucial data you really need, this is a possible way to get your hands on it. But it does require a working version Windows, and some storage on your computer (at least 10GB).
Hope it helps, until an update is issued.