In reply to neo.

The code that furnishes that error does a remote request using a Basic Auth header against the admin page with the file loaded. If fastCGI is enabled, for instance, the Basic Auth header won't get built or sent and that may be preventing the request from successfully retrieving the contents of the page.

All that to say, it's probably something in your server configuration that's preventing the page from being scraped and checked for fatals on submit.

It's easy enough to make the claim that it "worked before and now it doesn't" but the reality of the situation is that cowboy coding with no safety net worked before and now it doesn't, and that's a feature, not a bug.