Laravel/Illuminate Fatal Error - php

Question

I got a web app that works on my local computer, but not on my server. I get this error on server. I checked the code that the error mentions about, and there's nothing wrong with it.
Do you have any idea what causes this?
Thank you very much in advance.
Here's my error message:
Fatal error: Interface 'Illuminate\Exception\ExceptionDisplayerInterface' not found in /var/www/test-app.domain.com/public_html/vendor/laravel/framework/src/Illuminate/Exception/SymfonyDisplayer.php on line 6
Here's SymphonyDisplayer.php's line 6:
class SymfonyDisplayer implements ExceptionDisplayerInterface {
It says that there's no ExceptionDisplayerInterface. However, it's right next to this file, in the same directory. ExceptionDisplayerInterface.php is in Exception folder with SymphonyDisplayer.php
Here's my composer install output:
>>composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.
Problem 1
- jeremeamia/SuperClosure 1.0.1 requires nikic/php-parser ~0.9 -> no matching package found.
- jeremeamia/SuperClosure 1.0.1 requires nikic/php-parser ~0.9 -> no matching package found.
- Installation request for jeremeamia/superclosure 1.0.1 -> satisfiable by jeremeamia/SuperClosure[1.0.1].
Potential causes:
- A typo in the package name
- The package is not available in a stable-enough version according to your minimum-stability setting
see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> for more details.
Read <http://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.
Here's a new error after executing composer update:
Fatal error: Interface 'Whoops\Handler\HandlerInterface' not found in /var/www/test-app.domain.com/public_html/vendor/filp/whoops/src/Whoops/Handler/Handler.php on line 17
Here's some more outputs while trying to figure out the problem:
>>composer diagnose
Checking platform settings: OK
Checking git settings: OK
Checking http connectivity: OK
Checking composer.json: OK
Checking disk free space: OK
Checking composer version: OK
>>composer self-update
You are already using composer version 0d4c2bb7d7a864a9b3e876908e743310cdeaa5e6.

Answer 1

Phew. I fixed it.
Here's how I did it, if anyone else sees this type of error message:
rm -rf vendor && composer update -v
I guess my vendor directory went nuts while I was doing some stuff with SFTP yesterday.
Thanks everyone.