hummingbird gzip compression does not work (apache2 ubuntu 14.04 chrome browser)

After enabling gzip compression site no longer works:

* instead it shows 500 internal error with “Invalid command ‘Header’, perhaps misspelled or defined by a module not included in the server configuration, referer:” in the apache log file

* after I comment out “Header append Vary User-Agent” in .htaccess, site will work but hummingbirds shows “gzip is not working properly.

There is only motopress plugin installed and activated.