502 Bad Gateway in Backend

Manolo54

Hello Dear Fuel CMS Users

I'm really desperate and I was hoping you could help me out of my misery.
After looking through several threads about FUEL CMS having 502 Gateway Errors, none of the solutions listed were working for me.
Though I did raise the memory limit and buffer, the error still keeps occuring in the backend. (Rest of the site is fine).
Only when I deactivate my proxy-server, Nginx will stop giving me 502 errors, but I can't solve the problem that way, as there are more sites than just this one my server and I can't just deactivate it for all the other sites.
Has anyone gotten an idea how to solve this problem without having to reinstall Fuel CMS and said website altogether?
As said: Error only occurs in the backend. Could it be that my administrationpanel is corrupted?
What else to know:
- Error didn't occur right away after the site being online, it only started some month later.
- Since Fuel CMS was installed I'm having an unusual large amount of HTTP-Traffic (Apache Server).
- Again: Error only in backend/administration panel

Thank you very much beforehand!
I hope we can solve this problem!

Greetings
Manolo

admin

What were the proxy buffer size increases. We have used Media Temple's DV which uses Nginx in front of Apache and we'll use something like the following.
proxy_buffer_size 16k; proxy_buffers 32 16k; proxy_busy_buffers_size 64k;

This is usually caused by too big of a header size which a lot of time means that their is a cookie that is too big. Does the error go away initially if you delete the ci_session and the fuel_... cookies? You could try also to save the session information in the database:
http://ellislab.com/codeigniter+/user-guide/libraries/sessions.html

Also when you say an unusual amount of large HTTP traffic could you provide more details (what files, how much etc)?