Got this solution from the SW tech support team at SolidWorks World 2015:
This is a file association error. Here are the steps:
1. Shift-right click on the SoldWorks icon on the desktop.
2. Select Run as adminstrator.
3. Select Settings/File explorer.
4.Select Restore file association.
Thanks, -Dave Ellert
Dave Ellert wrote:
I have not updated for service packs, because I want to stay on the same version as my students for troubleshooting, etc.
I'm glad you got it figured out. And by the way, installing up-to-date service packs for the same version won't cause problems with compatibility. That only happens when you update to a newer version, such as going from SW2014 to SW2015. I know that's true for the commercial version, and while I'm not familiar with the Student Version I would assume that the same is true for it as well.