ChromiumOS update error

localhost / # update_engine_client --update --omaha_url=http://chromebld.arnoldthebat.co.uk:8081/update
[0923/091515:INFO:update_engine_client.cc(646)] Forcing an update by setting app_version to ForcedUpdate.
[0923/091515:INFO:update_engine_client.cc(648)] Initiating update check and install.
[0923/091515:INFO:update_engine_client.cc(674)] Waiting for update to complete.
LAST_CHECKED_TIME=1411456515
PROGRESS=0.000000
CURRENT_OP=UPDATE_STATUS_IDLE
NEW_VERSION=9999.0.0
NEW_SIZE=342053894
[0923/091521:ERROR:update_engine_client.cc(385)] Update failed.