2.6 does not support PHP 7.
https://book.cakephp.org/2.0/en/installation.html#requirements
Seems you’ll need to upgrade to at least 2.8 to get support for 7. (It’s not clear from that page which versions support 7.2 vs 7.0.) This will likely require some code changes on your part; I don’t know as I skipped straight from 1.x to 3.x. Migration guides for 2.x are here:
https://book.cakephp.org/2.0/en/appendices.html
See also this topic: