Error on activation

I followed the instructions at https://premium.wpmudev.org/project/who-sees-ads-for-wpmu/installation/ and got the following error when I activated the plugin.

Warning: require_once(/hermes/bosweb/web020/b209/host/webfolder/wp-content/plugins/whoseesads/whoseesads_admin.php) [function.require-once]: failed to open stream: No such file or directory in /hermes/bosweb/web020/b209/host/webfolder/wp-content/plugins/whoseesads/whoseesads.php on line 347

Fatal error: require_once() [function.require]: Failed opening required '/hermes/bosweb/web020/b209/host/webfolder/wp-content/plugins/whoseesads/whoseesads_admin.php' (include_path='.:disappointed:usr/local/lib/php-5.2.17/lib/php') in /hermes/bosweb/web020/b209/host/webfolder/wp-content/plugins/whoseesads/whoseesads.php on line 347