We have a several jobs are failing to deploy artifacts after successful build.
In some cases the build is successful and the log looks like:
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 36 minutes 18 seconds
[INFO] Finished at: Sun Oct 03 12:06:29 IST 2010
[INFO] Final Memory: 162M/461M
[INFO] ------------------------------------------------------------------------
Sending e-mails to: ttt@xxx.com
channel stopped
Archiving artifacts
FATAL: null
java.lang.NullPointerException

In this case the artifacts are archived and appear on the build page, so I assume it fails on the deploy step, no artifacts are deployed.
---------------------------------------------------
Another case (same job, another build):
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 50 minutes 48 seconds
[INFO] Finished at: Sun Oct 03 14:44:43 IST 2010
[INFO] Final Memory: 117M/306M
[INFO] ------------------------------------------------------------------------
Waiting for Hudson to finish collecting data
Sending e-mails to: zz@vv.com
ERROR: Processing failed due to a bug in the code. Please report this to users@hudson.dev.java.net
java.lang.NullPointerException
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project.getRootModule()=hudson.maven.MavenModule@224d3857[Nightly-15-yyy/com.xxx.yyy:yyy]
FATAL: null
java.lang.NullPointerException

In this case build appears as Failed