Help! Blank page with message on editing page properties

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I'm using Concrete5 5.4.1.1 for a site on my localhost.

1 - When I edit page properties from the Edit Bar, the properties update, but I get a blank page with the message {"cID":"70"}. The url page ishttp://localhost/mysite/index.php?cID=70&ccm_token=1305874786:0...

2 - When I edit page properties from the Dashboard Sitemap, the properties update, but I get a blank page with the message {"rel":"SITEMAP","name":"mypage","cID":"70"}. The url page ishttp://localhost/mysite/index.php?cID=70&ccm_token=1305874952:c...

Is this a bug, a misprint, a test?
What can I do to avoid it?

Thank you.