I had the same fatal error when I logged into my sites admin page after v 2.16.1 auto updated.
This is what fixed it for me.
I downloaded the zipped 2.16.1 plugin for Sermon Manager and uploaded it to my ftp/incoming directory.
I deleted the existing Sermon Manager plugin directories. I then moved the freshly unpacked Sermon Manager directories into the plugin directory.
After I did this I was able to login to my admin page without the error. I may have had to activate the Sermon Manager plugin.