No data Received on Popups

Hi there I am having issues with suitecrm in that when I click on an item say in a target list, I want to add an account or contact or lead doesn’t matter which I get the error.
No data received
ERR_EMPTY_RESPONSE
Unable to load the web page because the server sent no data.
here is part of the url that is shown on the popup
https://www.mywebsite.co.uk/crm/index.php?module=Accounts&action=Popup&hide_clear_button=true&mode=MultiSelect&create=true

It does however work if i was to select a user instead.
I tried this in the accounts as well to select a contact with same results.

I have tried quick repair, reset permissions to 777 on the cache folder, (i notice some folders within are set to 2777)
config.php and config_override.php are set to 775

any help would be much appreciated.

Hi, Trying to fix whats going on I have tried reinstalling SuiteCRM 7.5.1 with same results, so built a new ubuntu 14.0.4 server Apache/2.4.7 - php 5.5.9 - mariaDB installed versions 7.5.1 and also 7.4.3 but get the exact same results so not sure what is going on, if I use suitecrm demo site everything i am trying to do works.

This is rather urgent so any help would be great
thanks
jamie

Well I managed to fix the issue, it appeared to be an issue with memcached, so I added -B binary to the memcached.Conf file restarted the memcached service and all was good. I found the error in the apache error.log file.