try re-installing it and use the codes below,

composer install

for fresh install don't use the codes below,

composer update

Are you using XAMPP? or MAMP? or WAMP or Laragon?

Hi, Iridion.

I get the same error using 'install' for new fresh installation. I'm using

composer update

for install html/form helper package.

I'm using LAMP (linux -archlinux-, apache -2.4.12-, mysql -mariadb- and php).

Strange, because the mcrypt extension works normally. Is possible make a install/update ignoring the system's dependencies?

Thank you for reply.

Perfect! That works.

Simple add mcrypt extension in:

/usr/share/php-composer/php.ini

and

NoUpgrade = usr/share/php-composer/php.ini

In '/etc/pacman.conf' for no change this config file in future updates.

Thank you Jason.