One possible cause is a delay in a new App ID being propagated to the servers. I created an App ID and got this error for the first few minutes; then it started working.
The same
Please contact Wolfram|Alpha support team directly:
http://www.wolframalpha.com/contact.html
I got the same problem. I also cant compute anything in the browser version. Ill update if I find a solution. Hope it gets fixed :)
