Ran into this just this morning. I started up my Eclipse for Android environment and had all my projects greeting me with the error; “Debug certificate expired on 10/1/2011″. It’s an easy enough fix.
Delete your debug certificate under ~/.android/debug.keystore (on Linux and Mac OS X); the directory is something like %USERHOME%/.androidon Windows.
The Eclipse plugin should then generate a new certificate when you next try to build a debug package. You may need to clean and then build to generate the certificate.