When you try to run get the following error:
Re-installation failed due to different application signatures.
You must perform a full unistall of application. WARNING: this will remove the application data!
Please execute 'adb unistall X' in a shell.
It may be that the application is used in various equipment or certificate has been renewed. But surely it is because the certificates do not match (does not match that of the previously installed version and you want to install). It happens if you want to launch the same application but from a different project or moved.
This error may come from different sources. They are to provide solutions to each.
Solution for certificate renewal
A (recommended): Removing Emulator application and returning it to run from the Eclipse (Settings / Applications / Manage applications).
Mode B (if you do not mind losing all data on the physical device or emulator, you can not undo): Clearing the emulator and returning it to create. If a phone: erasing all data from the phone and leave it again as it was from the beginning (Settings / Privacy / Factory data reset).
Team change solution or by moving the project
If we are to move the project from one computer to another, we have to do to avoid problems is the following.
On the old computer go to "Windows / Preferences".
In the bar on the right select "Android / Build" and look at the path where the keystore is set to "Default debug keystore".
We go to the folder and copy the "debug.keystore" the new team (eg the desk of new equipment)
In the Eclipse of the new team back to "Windows / Preferences" and "Android / Build". In the "Custom debug keystore" field we select the keystores we brought the old computer. Press "OK".
Rerunning the application should work.
Note: if you give other failures by the certificate, other than look for expired certificate.