So, I installed Laravel on a dev server (php5.5.3, standard installation, mcrypt installed), and I get the following error message:
Fatal error: Class \'Illumina
Run this command:
composer update --no-scripts
In my case I have added another required package(Guzzle) in the compser.json file separately(in the last line but it should be after the laravel package line) and updated the compsoser and came across this issue.
I have checked and my vendor/laravel folder has gone. That was preventing me to run any artisian command.
So "--no-scripts" worked for me as it prevents any scripts to be included before executing artisan.
You can use another method in case you are having issues.