wp-supercache: You do not have sufficient permissions to access this page.

I’m pulling my hair out.

I had wp-supercache working perfectly before this last WP upgrade, now it’s not working. When I try to clear cache, or enable/disable the cache, I get “You do not have sufficient permissions to access this page.”.

I’m logged in as admin (the only user). I can’t figure out what’s going on!