For anyone that encounters this same issue, here is what the problem was:
My webhost (ipowerweb) changed the path for my dirroot and my dataroot. WIthout telling me, of course. To fix the problem, I had to go into my config.php and change the paths.
Glad it was a simple fix, but I had no clue what the problem was, given that the rest of the site was working fine. And, of course, without the knowledge that the webhost would change something like that.
Thank you to Howard, who advised that I turn on debugging. When I did that, and got the error posted above, I noticed the difference in the path (bosweb/web101 vs. bosoraweb168) and thought 'hey, does this mean I need to change my config.php?
Hope this can help save someone else a few days of frustration!