Pandora have unceremoniously altered their undocumented APi (written up for Windows Phone users by Justin Angel) allowing outside access to their service, rendering unofficial 3rd party apps like MetroRadio, Radio Controlled and WPFandora temporarily useless.
The developer of MetroRadio, Mustafa Taleb, notified us of the situation noting:
"The user can no longer login using the 3rd party applications. Message from Pandora's servers:"org.apache.xmlrpc.XmlRpcException: 000.000.000.000|0|INCOMPATIBLE_VERSION|Pandora does not support your client version."
Possible reason: They changed their encryption keys.
I am currently working on a fix and it should take me no longer than 2 days to update the app, and 5 to publish it."
That's certainly a bummer especially for us who have the MetroRadio Pro app. The good news is devs should be able to once again fix this issue and push out an update. Needless to say, it's a pain and would be easier if (a) Pandora just let 3rd party apps use their service or (b) they had an official app for Windows Phone.
There's no evidence that Pandora are changing these APIs on purpose to block apps but whatever their motivation that is the effect.
We'll keep you posted but in the meantime, you may want to try iHeartRadio which has similar Pandora functions.