Squid 502 bad gateway

[Mihail Z.]

Few days I have a trouble with accessing to the some web-sites through proxy (Squid 3.1.8 + squidGuard 1.4r4). I didn't make any changes in configuration. When I try to open some web-sites, browser shows to me page with "nginx Bad Gateway". Without proxy theese sites are opening normally. Google told me, that I'm not alone with this problem, but I can't find a solution.

Please, help me in solution of this trouble!