Google Map on Android

We have an application that uses google maps' api.

After following the tutorial on how to generate a keystore, fingerprint and api key here: http://code.google.com/android开发者_StackOverflow社区/add-ons/google-apis/mapkey.html. We have successfully run our application with maps showing.

But after sometime the map stop showing, I tried to create a new key using the same procedure but didn't work. Finally I tried creating on a new machine and it worked. Is anyone have any idea what's causing this problem?

Did you know that Google has limitation on request to be processed? While you run your application, how many request (roughly) google maps should serve then? Please checkout Google Maps API FAQ