502 Bad Gateway on only one page of Admin

[JohnHalsey]

Hello,

 

I am quite new to Prestashop.  We have a project which is being developed locally on a virtual box.  It works fine except we get a 502 Bad Gateway error page when I try and click on the Advanced Parameters -> Performance option in the Admin.

 

I am trying to access this page because we are making changes to the code in the files but it is not being updated on front end in the browser and are trying to clear the cache, and have seen many posts about it being in that menu option. The one option I cant get to.

 

I have access to the local database in phpMyAdmin and have already checked the ps_configuration table and the ps_smarty-cache, ps_css_theme_cache and ps_js_theme_cache are all set to 0.

 

Any help appreciated.  Going round in circles a bit.

 

Thanks