sorted it, modsecurity blocking it
if you have access to a webserver:
vi /etc/httpd/modsecurity.d/modsecurity_localrules.conf
Add:
SecRule REQUEST_FILENAME "/adminFOLDERNAMEHERE/*" \
"allow,phase:1,nolog,ctl:ruleEngine=Off"
(adminFOLDERNAMEHERE is the admin folder name of your site)
you should really use the full local server address in here, but if you use a few prestashop sites with the same admin folder name then this way would be much easier,
this should also fix any “501 Not Implemented” that occur when doing anything within admin if you have modsecurity enabled,
another option that might work for you is to add this to your .htaccess file in admin
SecFilterEngine Off
SecFilterScanPOST Off
but i think this depends on which version of modsecurity you have and didn’t work for me