Fatal error: error(s) during the installation of the files

Fatal error: error(s) during the installation of the files.
Unable to make '/var/www/vhosts/computer-base.net/httpdocs/acp' writable. This is a misconfiguration of your server, please contact your system administrator or hosting provider.
PHP warning in file /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/io/File.class.php (53): fopen(/var/www/vhosts/computer-base.net/httpdocs/acp/update_edithistory.php): failed to open stream: Permission denied


Information:id: d82ed07a4c3cd2de83d5d2f6ca816c1fc6f68a6d
error message: error(s) during the installation of the files.
error code: 0
file: /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/setup/Installer.class.php (168)
php version: 5.3.3-7+squeeze17
wcf version: 2.0.9 (Maelstrom)
date: Mon, 03 Nov 2014 04:40:27 +0000
request: /acp/index.php/InstallPackage/?&
referer: http://computer-base.net/acp/index.php/PackageUpdate/?


Stacktrace:#0 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/setup/Installer.class.php(56): wcf\system\setup\Installer->install()
#1 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/package/PackageInstallationDispatcher.class.php(644): wcf\system\setup\Installer->__construct('/var/www/vhosts...', '/tmp/files_6e62...', Object(wcf\system\package\FilesFileHandler))
#2 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/package/plugin/FilePackageInstallationPlugin.class.php(50): wcf\system\package\PackageInstallationDispatcher->extractFiles('/var/www/vhosts...', '/tmp/files_6e62...', Object(wcf\system\package\FilesFileHandler))
#3 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/package/plugin/AbstractPackageInstallationPlugin.class.php(71): wcf\system\package\plugin\FilePackageInstallationPlugin->install()
#4 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/package/PackageInstallationDispatcher.class.php(557): wcf\system\package\plugin\AbstractPackageInstallationPlugin->update()
#5 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/package/PackageInstallationDispatcher.class.php(140): wcf\system\package\PackageInstallationDispatcher->executePIP(Array)
#6 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/acp/action/InstallPackageAction.class.php(72): wcf\system\package\PackageInstallationDispatcher->install('356bdd77')
#7 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/action/AbstractDialogAction.class.php(70): wcf\acp\action\InstallPackageAction->stepInstall()
#8 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/action/AbstractAction.class.php(49): wcf\action\AbstractDialogAction->execute()
#9 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/request/Request.class.php(58): wcf\action\AbstractAction->__run()
#10 /var/www/vhosts/computer-base.net/httpdocs/wcf/lib/system/request/RequestHandler.class.php(108): wcf\system\request\Request->execute()
#11 /var/www/vhosts/computer-base.net/httpdocs/acp/index.php(10): wcf\system\request\RequestHandler->handle('wbb', true)
#12 {main}