After you install the Android SDK in Eclipse, it generates a debug signing certificate for you in a keystore called debug.keystore. The Eclipse plug-in uses this certificate to sign each application build that is generated.

Now, the problem with this debug certificate is that it is only valid for a year, or 365 days. If your Eclipse IDE uses an expired debug certificate, you will not be able to create and/or deploy an Android app.

To fix this problem all you need to do is delete the debug.keystore file.

1. Go to Preferences
2. Android
3. Build
4. Default debug keystore

There you should see the folder where the file is located. Simply delete that file and you are good to go.