Johny, if you stuck on maintenance mode, you can sign-in to your website by going to www.site.com/sign-in

Take a look at  public function coreUpdate() function of plugins.php file.
Your update fails somewhere here:

 $archivePath = OW_DIR_PLUGINFILES . 'ow' . DS . 'core.zip';
        $tempDir = OW_DIR_PLUGINFILES . 'ow' . DS . 'core' . DS;
        $ftp = $this->getFtpConnection();
        $errorMessage = false;
        OW::getApplication()->setMaintenanceMode(true);
        $this->pluginService->downloadCore($archivePath);

        if ( !file_exists($archivePath) )
        {
            $errorMessage = $language->text('admin', 'core_update_download_error');
        }

Overall script just was not able to download an update pack into specified directory ( DIR). There could be a lot of reasons why.
1. Check whether you have ow_pluginfiles/ow directory.
2. Make sure that you have 777 permissions for both and overall whole ow_pluginfiles directory should have 777 permissions set recursively.


As a solution I suggest performing core platform update manually.

Topic was moved from Installation Troubleshooter and Server setup.