500内部服务器错误Laravel 4

我在Laravel 4中有一个项目。它在比特桶上。我已经从本地机器上的回购中下载了它，装入了本地虚拟主机，运行良好。但是，当我在服务器上克隆了同一个项目并创建了一个虚拟主机时，会显示500内部服务器错误。在同一个域上，laravel 5中同一项目的另一个虚拟主机运行良好。

这是我为laravel 4项目编写的虚拟主机文件代码：

<VirtualHost *:80>
    ServerAdmin webmaster@localhost
    ServerName l4.mydomain
    ServerAlias l4.mydomain
    DocumentRoot /var/www/L4/public
    <Directory /var/www/L4/public/>
            AllowOverride All
    </Directory>
    # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
    # error, crit, alert, emerg.
    # It is also possible to configure the loglevel for particular
    # modules, e.g.
    #LogLevel info ssl:warn
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
    # For most configuration files from conf-available/, which are
    # enabled or disabled at a global level, it is possible to
    # include a line for only one particular virtual host. For example the
    # following line enables the CGI configuration for this host only
    # after it has been globally disabled with "a2disconf".
    #Include conf-available/serve-cgi-bin.conf
</VirtualHost>
# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

这是laravel 4项目的.htaccess代码：

IfModule mod_rewrite.c>
  <IfModule mod_negotiation.c>
    Options -MultiViews
  </IfModule>
  RewriteEngine On
  # Redirect Trailing Slashes...
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule ^(.*)/$ /$1 [L,R=301]
  # Handle Front Controller...
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteRule ^ index.php [L]
</IfModule>

我还将"index.php"更改为644权限，但没有使用

这是在日志文件中发现的警告和错误：

PHP Warning:  require(/var/www/myproject/bootstrap/../vendor/autoload.php): failed to open stream: No such file or directory in /var/www/L4/bootstrap/autoload.php on line 17

PHP Fatal error:  require(): Failed opening required '/var/www/myproject/bootstrap/../vendor/autoload.php' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/L4/bootstrap/autoload.php on line 17