Super Cache used to work for me - but then I uninstalled and reinstalled it (for an unrelated reason) and it no longer caches my pages.
From the debug, it looks like it has to do with a missing closing html tag. I've seen all the other suggested solutions, but since this plugin worked for me in the past, I don't see how there could be a theme or plugin conflict? Unless something accidentally changed?
Is there a way to identify the exact location of the error?