Igor, here are the logs from the panel, showing the error:
2015/05/07 13:31:51 [error] 52544#0: *1434 upstream timed out (110: Connection timed out) while reading response header from upstream, client: xxx.xxx.xxx.xxx, server: , request: "POST /smb/web/change-hosting/id/23 HTTP/1.1", upstream...