Thread:Project:Support desk/Content Encoding Error after Migration/reply (13)

Read this, it's likely your problem. Again, the fact that when an article is not present and MediaWiki issues a HTTP 404 response, the server intercepts it and changes the output to its custom error page demonstrates that's not a MediaWiki issue:

http://till.klampaeckel.de/blog/archives/148-nginx-configuration-gotchas.html