[2.0.8 Community] error 500 with nginx, 502 with apache2

I am currently working for a customer to update a website from static html to Joomla.
The customer wanted to have responsive design without changing his main one - so I installed Joomla Mobile Community as a tech preview.

This has worked for a week or so, but today, I get the error 500 on nginx, or 502 when on apache2.

The Server log just says:
[Fri Sep 25 06:31:24.492901 2015] [fcgid:warn] [pid 7281] (104)Connection reset by peer: [client (ip):46317] mod_fcgid: error reading data from FastCGI server
[Fri Sep 25 06:31:24.493007 2015] [core:error] [pid 7281] [client (ip):46317] End of script output before headers: index.php

This only happens, when "Mobile_Basic" theme is selected, and the page is viewed with a mobile device.
Any other template works fine.

Due to the fact that the customer hasn't yet acknowledged the changes, I need to fix this really fast, but I don't know how.

Best regards, Dirk

Could you post (or PM) the list of system-type plugins used on the website?

And what Joomla version do you use?

Is there error messages in PHP's error_log (if it is separated from global one)?

Could you check version attached to www.mobilejoomla.com/forum/26-mobile-joomla-2x/19468-small-error-when-using-nginx-as-webserver.html#19474 ?

Fixed in MJ 2.0.10.

I am sorry to say this, but the customer has seen this issue and insisted to use another solution for responsiveness...
The version is Joomla 3.4.4 with german translation.
OSMap, SEO Glossary and JCE Editor have been installed...
Thank you for you're help.
Dirk