I’ve tested this from my local PC via the php api with the same results, here are the request headers for both results:
Working via GUI: http://52.11.187.148/result/150515_WV_6/1/details/
GET / HTTP/1.1
Host: www.chroniclelive.co.uk
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36 PTST/210
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8
Response Headers:
HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Content-Encoding: gzip
Content-Type: text/html;charset=UTF-8
Server: nginx
X-Cache-Hits: 2
X-Cacheable: YES
X-ProcessESI: yes
X-RemovedCookies: YES
X-Served-By: reg-cache1a.tm-aws.com
X-Varnish: 874910373 874904503
Content-Length: 39427
Cache-Control: max-age=4
Date: Fri, 15 May 2015 12:22:06 GMT
Connection: keep-alive
Set-Cookie: stop_mobi=true; path=/
Vary: Accept-Encoding,User-Agent
============================================================================
Failing via API: http://52.11.187.148/result/150518_0Z_8/5/details/
GET / HTTP/1.1
Host: www.chroniclelive.co.uk
X-Jpeg-Mode: 2
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8
Response Headers:
HTTP/1.1 403 Forbidden
Server: nginx/1.4.6 (Ubuntu)
Date: Mon, 18 May 2015 12:11:57 GMT
Content-Type: text/html
Transfer-Encoding: chunked
Connection: keep-alive
Content-Encoding: gzip