immanence, thanks for the info. You’re exactly right–the new version requires Apache 2. I was running 1.3.42, also on a shared host.
I would have expected this to be clearly stated, or that the plugin itself would check the version of Apache prior to updating.
I was forced to restore from a backup as well.
I’m done with S2. Fix or no fix, this kind of carelessness on the part of the developer leaves me unable and unwilling to trust their code in my site any further.