This error can have multiple causes. Some are explained on our sister site, in Error while retrieving information from the server RPC:s-7:AEC-0 in Google play?:
turns out my credit card info on file needed updated to my new expiration date.
is one possibility. One more:
RPC:AEC:0 error is known as CPU/RAM/Device/Identity failure.
- Go to settings >application > Play Store >Clear Data & Clear Cache.
- Go to accounts >Google >Remove account.
- Reboot device.
- Again Settings>Account >Google >Log In.
Another reason is explained on AndroidPIT (German): It could be problems with Google servers (same is, btw, reported by users in this thread on AndroidForums.Com). One user reported a work around that did it for him: He tried it at least 10 times on his Android device, without success. So he simply fired up the browser on his computer, and tried it from there -- which immediately worked.
For more details (and possible other solutions/work-arounds), just follow the other results from this Google search.