This is fixed by writing to the "[email protected]" mailing list, describing the problem and the particular machine.
You can see the machine the build is running on in the upper right corner of the Jenkins status page. Infra usually fixes by "rebooting" the machine. Yesterday these builds were failing on H29, which has now been rebooted. This morning, my build is running on H44, so I can't confirm this fix worked... -Marshall
