Please be aware that this discussion dates back from September 2013.
If you are receiving a sign-in error then please try removing the OPM.db file per solution 2 in CC desktop lists applications as "Up to Date" when not installed - http://helpx.adobe.com/creative-cloud/kb/aam-lists-removed-apps-date.html.
In addition I have personally installed questionable virus protection software which has caused this exact same behavior to occur. I would recommend also reviewing Sign in, activation, or connection errors | CC, CS6, CS5.5 - http://helpx.adobe.com/x-productkb/policy-pricing/activation-network-issues.html and try temporarily disabling your security software to see if the same behavior continues.