I have installed CakePHP 2.0 framwork using steps below:
1. Start the terminal
2. sudo mkdir /var/www/cakephp
3.sudo cp -r ~/cakephp/* /var/www/cakephp
Using chmod -R 777 /var/www/cakephp/app/tmp/ i.e. making folder execuatble will solve this issue. I even faced similar issue while testing cron i.e. shell which exists in app/Console/Command/ folder. When we execute a cron multiple time, tmp/ folder permission is overwritten and permission error will come in picture at this point which can be avoided by making tmp/ folder executable recursively.