The lib/ext/dnsns.jar jar is erroneously duplicated in Kernel -- it is both included verbatim in "core", and then defined as a separate "dnsns" bundle.
In most situations this is harmless, as the downloaded jar will simply overwrite the existing one. But if the jar is accessed, and then Kernel is asked to download the dnsns bundle, the download will fail due to an inability to overwrite the jar.
To reproduce, perform the steps listed in 6645408. This is a regression introduced since 6645408 was filed, and will have to be fixed first.