Answer by Girish Patel for "Debug certificate expired" error in Eclipse Android plugins

To fix this problem, simply delete the debug.keystore file.

The default storage location for AVDs is

In ~/.android/ on OS X and Linux.

In C:\Documents and Settings\.android\ on Windows XP

In C:\Users\.android\ on Windows Vista and Windows 7.

Also see this link, which can be helpful.

http://developer.android.com/tools/publishing/app-signing.html