Right here was my problem:
If you have done everything correctly, ie change file permissions and checked there is no conflicting plugins then the reason is likely to be the same as mine.
Check you php.ini file - If php safe mode is on turn it off.
If you can’t access your php.ini file, you might be able to create one in your directory or alternatively ask your web hosting company. You may only be able to edit it through SSH in which case read my article on SSH commands and VI commands.
If you have access to your domain through a plesk control panel sometimes you can turn it off in the domain setup page. When you add a new domain to the server and tick the php box, the php safe mode box is automatically turn on.