works ok for me
do you have part/assembly templates specified in your options?
AHA! This was my problem. In teh SolidWorks system options, I had default templates for Parts and Assemblies specified. When I changed this to "prompt user to select template", and then tried to open the STEP file, it worked! I don't understand why it wouldn't work with the default templates, as that is what I selected when prompted anyway, but oh well. Thanks!