Page Manager Error: The requested page "/xxxx" could not be found
Are you using the stable version of the ctools and panels module, this error doesn't seems to be in the issue queue of the respective modules.

As @David as mentioned the problem could be of selection rule or the access rule.

Have a look at the use tutorial for creating the page with page manager: http://nodeone.se/en/learn-page-manager-part-1-overview

Also check the documentation of the page manager module: https://drupal.org/node/1862908