Thank you for the feedback and the quick fix. On one of the websites, I cannot activate (or delete) it anymore, as this gives a fatal error. I was able to update from 3.8.0 to 3.8.3, though.
I deleted all apcm entries in the database. Still, when I try to activate, it says “Plugin could not be activated because it triggered a?fatal error.” And then I try to delete, it says, “Deletion failed: There has been a critical error on this website.Learn more about troubleshooting WordPress.”
Deleting through FTP obviously works. Any ideas how to fix it?