My first port of call would be to make sure that you have all the appropriate modules enabled for your server. For example, on a LAMP stack:
In your apache’s http.conf the following lines would need to be uncommented
LoadModule expires_module modules/mod_expires.so
LoadModule headers_module modules/mod_headers.so
LoadModule mime_module modules/mod_mime.so
You would need to restart your apache server for this to take effect