Site loads with unwanted characters for guest users when “W3 Total Cache” is defined in wp-config.php

Question

When a user is logged in, site loads without any problem but if a guest user visit the site, it shows some characters same as this:

O-y²ee·¹”s<$+¼š[ÌÙtõBÉf2ŒÉ& ÙW!Ìèe Ôð9â§ÃGežÀœäì {ËuíΈFòf©D ¢k’t}8ƒEm¿TePYâsáÂq¯‚—cˆ#Ñ›>Ælæ#u«lB,G«gƁ¯æÚå¿—TYûKä!E"¢ØÀÕìS<ðEùànú0"¸µq8ÜW1K™1ìµPóåÄ8D²ŠmmâP¦lËJzñC¥R#Íñ&À…¦Z0D"†˜y‘„¡«vb›‡l1yZ>ÑʬnìÛÉ«âÅV7±³ W+Š

and nothing else shows

Im using Q2A with wordpress integrated

 

Edit:

I found that Q2A get in trouble when I define "W3 Total Cache" in wp-config.php