ERROR [Emergency]: Uncaught TypeError: Return value of Symfony\Component\Filesystem\Filesystem::toIterable() must be an instance of (...)

[rbaarsma]

When doing a fresh install I get multiple errors, the first of which is in the title of this bug post.

see silverstripe/silverstripe-asset-admin#703

Basically symfony/filesystem requires php version 7.1.3 or higher.

So simply add "php": "^7.1.3" to composer.json to fix this for others

[rbaarsma]

Possible duplicate of silverstripe/cow#65

[robbieaverill]

Have you installed using one of the archive files from the SilverStripe website? If so, they can be built for PHP 7. You can run composer update from within your project to downgrade these dependencies to PHP 5.6 compatible versions if you're not running PHP 7. I'm going to close this because we have a couple of duplicates at the moment, but thanks for raising the issue